EPTTo reintroduce the medic:
To reintroduce medics would have vast complications to the late game, where a good chunk of your army would be in healers that take up space from your ground army. Which could render some of your army units to not be firing because the medics is in the way. So the late game terran bio army could be significally weaker. Also your healers would now also be under fire by the colossus, so they would get killed more easily. Also this necessitate a higher barrack count since you have to reproduce healers, since you lose them more easily. I think you accounted for this by introducing upgrades that would make them stronger than medivacs but I feel that those upgrades do not break even with the downside of a ground healer(medic).
Against zerg it would have same problem since fungal and banelings will now kill off your healers aswell.
However there is a big con with having a healer from the barracks which is the time you can get healers onto the battlefield. Building and gas investment for medivacs is quite hefty for them to be out on the battlefield for any early game push.
Perhaps buffing the tanks is unnecessary:
When it comes to tanks I do not believe you have to buff them to make them viable in TvP. I think you nailed it with the re-designed immortals. By adjusting the immortal to not be a complete counter to mech, will make mech viable and not as useless in the midgame. Of course mech will still suffer from immobility but that is your sacrifice for having an inbreakable army. There is just one thing I would change with your immortal, which is that hardened shield would not be removed but it should be tweaked so that it reduce all damage greater than 25 to 25. So its shield would absorb 2 siege shots or one thor shot. Which would make better against siege tanks but not change them against low tier units, and thors still kill them i 3 shots. In large army battles they still be not as great, since you would have critical number of tanks to take them down.
The rest of your purposals I do not have a well-defined opinion on yet so I will not discuss them for now.
# Edited: grammar and misspellings.
