In my mind the main flaw of the current system is that after getting a few band-aids, the soldier is "as good as new".
Therefore, in my mind the most straightforward change would be:
treated wounds != healthy
Treated wounds would not be getting worse, but they would still need to be healed in hospital.
And stats would depend on the healthy part.
I think it would do the trick.
I might be willing to specify this kind of wounds (generic wounds, not wounds-by-bodypart which is imho too complicated), with blood pressure bar and without, and post it here for public review and input (I don't believe very much in such kind of spec coming from the top of the head of one person).
That is, if someone is interested in implementing a wounds system and would find such spec useful, either as a spec for implementing generic wounds, or even as just another opinion about the wounds system (= for diversity).
(I might do some battlescape GUI things, but I am definitely not going to dive into the C part of the game)