I don't think it's all that overpowered. Remember, it gives less health if it is damaged, so wearing the stuff all the time would be wasteful. Figure you'd have the next move when you came back from the dead, but you'd also be naked and if there was only a few % left on the armor you're still in a lot of trouble. Sure, you could make nanofiber armor but then you're using up two power mods and walking around in slow, weak armor.
Maybe the armor would need to be a little weaker. No resistances, a little more slowdown. Also to compensate for the fact that it is unmoddable and supposed to be better than regular medical armor, maybe the medical power armor could also give a few seconds of invincibility when it kicks in.
ANyhway I'm just throwing ideas out there. I'm glad you like it, Kornel--maybe you guys could iron out the details a little. I definitely think it has potential.