Exactly, they tested an improved version of the T45-d Power Armour that would automatically heal the user; given that the T45-d was then replaced by the T51-b we can guess that nothing came out of it. That was a modification to an existing model and still doesn't give any reason why Power Armour would be researched at Big MT when, again, Power Armour was being developed by one company, West-Tek, which held all of the contracts and given the state of the war and the insanely expensive projects like the Vaults the Government didn't have money to throw at everyone when current models were largely sufficient. The medic prototype was just that, a prototype, from which we can clearly see nothing substantional came.
Big Mountain did plenty of research for the army as well - the giant robo-scorpion, nightstalkers, and the sneak suit were all originally intended for use in the war going by the various logs scattered around the Big Empty.
Besides, there was a securitron factory despite them having an institutional feud with RobCo. Clearly they're not above pirating other peoples' tech.
Honestly, the Big Empty is the most technologically advanced place we've seen in Fallout so far. It feels very disappointing that there's no PA.
Hell, I would have settled for the ability to rip the sneak suit's voice and stimpak dispenser out of that suit and cram it into my remnants PA and taken
that as my "new" power armor.

The new Stealth Suit enhances speed, reflexes and mobility, comes with a built in medical system and integral stealth systems. By any other metric other than "big, slow and bulky" the Stealth Suit Mk II is a set of light powered armor. Stop standing atop a rock with a minigun and embrace the glory of silent running.
There's already plenty of armor for sneaky characters - the Dragoon suit, the assassin suit, the Sierra Madre reinforced armor and Graham's vest (no bonuses to sneak, but they have a hell of a lot of DT for light armor, and light armor is better at sneaking...)
Characters who like heavy armor and power armor though... We don't have much. Brotherhood PA, that nets you kill on sight orders every time you come within view of the NCR. Ugly green T-51b PA. T-45d suits that don't provide much more DT than high end combat armor
and take away two agility. The only decent suits of PA in this game are Remnants PA and its derivatives.
And non-powered heavy armor guys are just left totally out in the cold. They've got metal armor and reinforced metal armor, with HH they get gecko versions of these suits that look identical but have some more bonuses and that's it.