Some background necessary:
I played SC since around 1998/1999. I played all three races in Brood War at a decent level, getting to around B- or so on iccup at one point as random (in SC1 playing random was about 10x more difficult than SC2).
Just a bit of meta game background that i can fondly remember from when i was a noobie first starting to play SC1 online in BGH pub games:
I remember a game of BGH i was top left playing Terran and it was a 4v4. Back then, RTS was so new and concepts of playing optimally were non-existent. People didn't even understand basic concepts as walling off our bases with buildings lol.
Vultures in those n00b games were considered a trash tier unit (i know this sounds fucking hilarious). Eventually...like most players that wanted to get good i moved onto "low money maps" with a USEast clan.
As it turned out, vultures were one of the most necessary units in the game to play versus Protoss, and by our communities standards today, if we could go back in time, all of us would be yelling and screaming "OP OP NERF VULTURES MINES IMBA" instead of just "getting better."
Vulture/tank/goliath was the go-to strategy versus Protoss, and in fact bio was literally not viable ever besides a 6 rax marine medic build that would be considered quite all-in. Reavers and psi storm, which were very strong in SC1, completely shredded bio.
99% of SC1 games were mech. But why did no one complain about this? Because games had constant action, harrassment, lots of bases taken, etc. The funny thing is, the definition of playing Terran was you were playing the turtle race - a lot of Terrans even took pride in being the defensive race. You kids today think the marine is the iconic Terran unit? Well, guess what - the most memorable and iconic unit of SC's history for Terran was the siege tank.
Siege tanks killed units - and they killed them hard. If there were 3-4 tanks up a ramp behind a wall, you could not simply "a-move immortals" into the wall take 20 tank shots, and somehow defeat defender's advantage. Instead what players had to do was MACRO. Take more bases, get money, make 20-25 gateways while Terran attempted to turtle with their badass tanks. And there wasn't anything wrong with that. Of course there were also spider mines and such in all of that, etc.
But most games were action packed ground versus ground affairs. Terran would amass an army of tank vulture and eventually goliaths and push out, while Protoss desperately took expansions, cleared out mine fields with dragoons and observers. Terran could push across the map with cheap 75 mineral missile turrets, mines, and tanks, and Protoss eventually started massing arbiters for mass recalls and mobility to do the equivalent of what would be a doom drop into the Terran's main, who would then try to counter that by patrolling science vessels along the perimeter of their bases to EMP incoming arbiters.
Mech was amazing to play, amazing to watch. But something very important was - you could attack with mech, you had that option, you had that capability. Siege tanks were strong to the point you could MOVE onto the map and trade effectively with your opponent's ground units.
And in the situation that Protoss decided to tech up into carriers...Terran could switch all 8-10 of their factories to goliath production which could compete equally against carriers through attack move micro or shooting down the carriers. This meant even if Protoss went air, Terran could still force action, MOVEMENT could happen. You didn't need to turtle for 30 minutes to deal with air units.
Mech eventually became the go-to vs Zerg late game as well...but all of the above that i have related is important to note because it highlights the main two issues that have plagued SC2 mech since this game has been released that i have highlighted for years, and tried to articulate to blizzard:
ISSUES WITH MECH PROBLEM 1:
-Siege tanks were gutted/nerfed in damage to the point it is sub-optimal to ever move out on the map with siege tanks because they will never trade EVER with the majority of units in SC2
http://wiki.teamliquid.net/starcraft2/Patch_1.1.0
The above patch utterly ruined an entire strategy for the majority of SC2 professional and casual play. And that patch was made to the game in a very short sighted way due to the old map pool having ridiculous maps like Steppes of War.
In addition to siege tanks being gutted in the above patch, throughout the course of SC2 patching other units/abilities/changes have been done to the game that make tanks worse and worse:
-adept shade
-warp prism buffs
-void rays
-tempest addition
-any mass air strat from any race forcing you to turtle to air
-LOTV economy
-list goes on
ISSUE WITH MECH PROBLEM 2:
-Mech has zero auto-attacking anti-air units from the factory that can be produced to deal with opponent's who make air.
As i related in my story about SC1 mech, a Terran could always switch all of his 8-10 factories to produce goliaths which not only were good, but competed so well with enemy carriers that in some games Protoss was even DISSUADED from massing more carriers.
What that meant is just the mere existence of the goliath swayed most SC1 games to be ground to ground ACTION PACKED affairs for both players.
In SC2, problem 1 of tanks sucking badly is made even worse when the opponent decides to be a smartass and start making any of the OP air units in SC2 - carriers, tempest, liberators, ravens, broodlords.
There is no unit from the factory that can compete with an opponent that masses air units. If the Protoss starts building tempests, he can simply begin to accumulate them from 0 -> as many as he wants and there is no factory unit to dissuade this from happening.
This then forces the "meching Terran" to sit in his base doing nothing for the next 10-20 minutes while he masses air units of his own, because only vikings/liberators/BCS can compete equally with enemy air units.
I made a thread about the issues of air units being too superior to ground units in SC2 a few weeks ago...i feel it has always been this way for mech, and now it is an issue in all match-ups in LOTV.
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I believe the above are the two core issues of Mech that have persisted throughout the entire lifespan of SC2 as a game.
They can easily be addressed, and could have been since years ago, and this is where my cynicism comes in - i do not believe blizzard will ever listen to the community, myself, or anyone about this - UNLESS you, me, the community will force blizzard to bring these issues up and address them.
They haven't listened for years, i am not hopeful they will now, but i suppose this thread is a last ditch effort to rally some of the SC2 community to get them to listen.
Some people think blizzard shouldn't bother with mech, and to those people i'd say you are hurting the longevity of SC2 by only wanting there to be 100% bio play viable for SC2. Other games like LoL are completely shitting on SC2 because those games get constant patch changes, champion updates, balance updates, ability updates, etc etc.
If you want SC2 to really compete and go on for many more years to come, you need to FUCKING DEMAND that blizzard pay attention to you as an SC2 player/customer/fan. You need to FUCKING DEMAND it. Not later, not a year from now, but NOW.
There should have been a fuck ton more patches and balance passes to SC2 throughout this games history, for balance, for strategic diversity, and just to even freshen up the game metagame-wise.
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Now for OPTIMISTIC AVILO:
In a world where blizzard listens and agrees that it's not OK for bio to be the only viable Terran strategy in every match-up. There are two things that need to happen:
ADDRESS ISSUE 1: SIEGE TANK STRENGTH
-Revert this patch in some manner
http://wiki.teamliquid.net/starcraft2/Patch_1.1.0
That patch is what screwed over mech from the very beginning, and made it so you basically can never attack with mech until you have 15 siege tanks...by then of course your opponent has 10 carriers/tempest and you now have to turtle another half an hour into mass raven/liberator/viking.
If tanks are made to be able to kill units and trade well again...to be a fearsome unit then a meching player can finally ATTACK the opponent, and even if the enemy catches you on the map - TANKS WILL TRADE. ACTION CAN HAPPEN. GAMES WILL BE FUN.
People's argument against changing the tank to not suck are: "But avilo...turtle mech will be fucking ridiculous!" And to that i'd say it's a faulty argument because turtle mech will remain exactly the same as it is now - the only way to play the game. Making tanks stronger doesn't suddenly make turtle mech stronger - people will still stylistically turtle regardless, and in combination with the LOTV economy that's already intrinsically addressed.
Buffing tanks to not suck will make it so mech games are ACTION PACKED instead of forcing you to sit in base and do nothing.
There are other directions blizzard can go, such as reducing tank to 2 supply and adjusting stats so that you could have more tanks on the field to make mech armies more fiercesome, although admittedly a tank change to 2 supply would require a lot more testing.
I firmly believe just putting the siege tank damage back to how it originally was would make SC2's metagame a lot healthier, would bring mech back in quite a good way. Test it blizzard.
Nothing crazy needs to be done such as overkill, or other BS changes. Just simply give the tank back it's power.
ADDRESS ISSUE 2: MECH HAS NO ANTI-AIR UNITS
-This has been the second issue forcing mech games to only be "turtle mech" games and blizzard and the community still refuse to listen for the longest time.
Mech needs a unit that can be easily and cheaply mass produced from the factory that can FIGHT VS AIR UNITS. If my opponent begins to amass an army of tempests/carriers cyclones/thors need to be a reliable way to dissuade my opponent from just simply "massing more air."
Buff mech anti-air so that a meching Terran can reliably build 5+ factories instead of having to turtle 30 min and sit in base massing air himself to counter air. This alone will make mech games action packed, and games will trend back to ground to ground instead of "oh im protoss he's going mech ill just mass infinity tempest/carrier now."
Obviously, i am suggesting that blizzard buff up the cyclone and thor to be much stronger versus air units, perhaps mines as well. However they do it, it needs to happen or mech will always suck and be "turtle into mass air" games.
ISSUE FOR ENTIRE LOTV: AIR UNITS ALL TOO STRONG FOR 3 RACES
Along these same lines...to re-iterate this thread i made a few weeks ago:
http://www.teamliquid.net/forum/legacy-of-the-void/496744-discussion-air-units-too-powerful-in-lotv
I truly believe air units need to be toned down for all 3 races so that games will trend towards action and trading of units rather than sitting back and massing an air deathball. Also ground anti-air should be toned up.
Tempest need a supply increase to 6 to dissuade simply massing them late game with high templar vs all races.
Ravens were already gutted.
Carriers need the release interceptor ability gone, they are already too strong when massed.
Liberators too strong when massed - though Terran being viable at all in LOTV currently resides on the liberator's back.
BCS suffer the same issue as carriers - useless in low number, too strong when you have 10+.
Vipers need a hard nerf - para bomb needs to go. Other abilities toned down in some way, energy costs maybe don't know.
Hydralisks need to be stronger versus air units. They suck when air is amassed.
INterestingly enough, Protoss ground anti-air is already pretty good with archon splash, stalker blink, and of course the ground AOE parasitic bomb known as psi storm

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There is my feedback about Mech in LOTV. There are a ton of other things i could have gone into, such as immortals/8 armor ultras/viper etc hard countering mech....but...
I feel the two core issues with mech are the one's i've highlighted:
1) Tanks sucking needing power back
2) Mech having zero anti-air that dissuades the other player from massing air, which then forces mech to sit and turtle for 30 more min into his own air
If tanks are given more damage it will promote action packed games of trading ground armies.
And if mech is given a strong anti-air unit, the same thing is promoted - both players trading ground armies since the opposing player won't just be able to simply accumulate their OP air unit as it will have a massable counter from cyclones/thors from mass factories.
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Thanks for reading, i have played Mech style since SC2 has come out - even during the WOL era where the marauder was considered a god unit and mech was considered a fringe strategy.
It still is, as most pro games in all match-ups are 99% bio play. I think blizzard should open up the mech option for Terran to create more play styles than just only bio.
Regardless, my last comment i will leave in this post for the entire SC2 community and what i urge everyone to do - please, please wake blizzard up to patching SC2 more often.
We all love this game. IT is the best game ever created, and SC literally is responsible for spawning e-sports itself in many ways. Blizzard should be patching this game constantly - not once every 9 months when people get rowdy. Gone are the development days of "patch it once and leave it alone for a year."
All game developers have moved on from this - SC2 needs patches when there are blatant issues such as adepts being OP but also should receive patches to liven up the game and keep the metagame fresh.
Final final words - please bring back Mech and strategic diversity to SC2.