EPTMech is a fundamentally very deathbally and incredibly strong composition-One could say it works almost like Protoss; Depending on hitting the critical number of units to achieve its maximum efficiency and assortment of AoE in its arsenal to deliver heavy punishment if directly engaged under ideal conditions.
With the new changes coming into LotV to force away from more deathball oriented builds, it is going to change the state of Mech drastically. Not only does Mech units cost a lot, its build time is very slow and its reinforcement methods very slow. At best there are reactor pumped Hellions/WM which aren't the best of reinforcements. It also has no real way to retreat if stuck in bad battle because of how immobile it is- thats the nature of mech. Mech is also very supply heavy, with siege tanks costing 3 supply-but harm from that would be explained next paragraph.
Of course, with new changes coming into LotV, it won't be doing any favors to this composition as the building times are both slow and expensive. Tank-dependant Mech play simply cannot handle being below critical number and be largely ineffective- it requires far too much resource and time to produce in sufficient numbers, which other compositions reach far faster, Mostly because of the nature of ranged army strength being multiplied exponentially as the numbers grow as explained in : http://www.teamliquid.net/forum/starcraft-2/465353-simple-combat-lanchesters-square-law.
With the new abilities coming into LotV to "encourage micro", it is simply going to punish innately stationary Mech play more than any other composition in game-without much to give back. Mech is already a composition that trades away its mobility but additional new abilities adding up to game wouldn't really justify much of sacrifice Mech does make for its power. It rather seems disproportionate. People have already seen that Mech is already rarely an option in TvP and among other matches due to its sheer immobility and available counters- Example seen with Chargelot-Archon-Immortal play which straight up hard counters Factory play as Archon takes reduced damage from all units bar WM and Thor (and bonus splash against hellbats), and Immortals straight up hard countering 2 of the units. Chargelots also take comparably reduced damage from what it has been before and has incredible survivability against tanks.
With immortal nerf brings up another case: its shield ability replenishes shield to extra 200 which would be hit to already rare TvP mech play with ghosts not being as effective in ghostmech composition than ever before. Immortals are actually looking to gain shield against Mech.
There is also case of Mech lacking in AA department and needing to rely on non-factory unit to solve that problem in form of vikings: But vikings are very filmsey and useless outside of its AA capabilities as it has no armor while having armored status just for sake of receiving damage. It current serves at best to act as very weak expensive buffer in emergency situations and doesn't really fill the hole goliath served. Cyclone is proposed but its lack of innate range and extreme expense doesn't do much.
Yes- you may argue that Mech is getting arguably a "huge buff" with siege tanks being allowed to be picked up in Mech army but that isn't serving much purpose to general Mech play. What purpose do those medivacs serve outside of it? Mech is insufficiently weak before its critical mass and all Medivac is going to do is to cut into army supply that could be used on other units while only being able to transport tiny fraction of units available due to cargo space mech takes. While it may increase the mobility, it isn't doing much to available firepower which decreases rapidly as numbers go south.
I am just asking that if there is going to be tradeoffs, make it proportionate to compensate the sacrifice. Right now, it may seem bit knee-jerky since LotV isn't even on beta yet, but it seems like with direction blizzard is heading, they may completely wipe off a variation of Terran play and choice when it is already rarely seen due to its disadvantage. It simply sacrifices too much for little in return at direction it is going now.
tl;dr:
-Mech is weak in smaller-medium numbers
-Sparse resource is only going to make it weaker with Mech not working very well before hitting critical mass
-other indirect nerfs encouraging faster play: see above
-Current buffs would buff Marine Tank style but serves as dead weight
-Cyclones don't really solve the AA weakness gulf Mech has
-Mech is looking to trade away quite a lot of its advantage in LotV for not much in return.
