I have been throwing a few unattainable ideas in my head recentwise; mostly because I don't have much desire to pursue them, because it's not really my kind of area of knowledge.
I did discover the other day that something similar had been done at one point, but apparently it was a completely broken obscure PC game so...
Well, basically, the gist of it is that y'play as a battlefield medic, but it's sort of conducted as a third-person ARPG. Rather than just being like a support class in any other shooter, the 'medic' part is the crucial thing here, ever played/heard of that DS game Trauma Center? Rather than just a 'press x to y' or quicktime event; the player is given a range of medical supplies and it's up to experience and briefings to learn how to best dress wounds, set bones or otherwise prepare soldiers for medivac; most importantly, you can fail.
I'm not so sure how an experience system would work, but typically it'd be less of a risk/reward system, and more of a player-choice-driven type thing; of course there would be rewards, but not always, the point is that you do what you choose to do under pressure, there's little time to consider the consequences.
You're given a .45 for self-defence, maybe you're thrown an M16 in combat, but the point is that you're a medic, therefore not all that good with a gun (I know that's hardly realistic, but...), or perhaps that could be a character creation balance, like intelligence against strength; you can choose to be a really effective medic (gives you more time to operate under fire, you get more supplies etc) or you can make the sacrifice of expertise to perhaps have more health, higher morale or concentration, or being able to move wounded behind the front line.
With the idea of a dedicated battlefield medic who ain't all that good with a gun either way sort of being quite unrealistic, the next point needs to be taken with a pinch of salt, but I kinda wanted to set it in Vietnam; divided between combat situations and spending your downtime earning money in Saigon (or similar), running packages, finding things, operating in the hospital/triage centres etc.
and that's murh idea; it'll never happen, but it's an idea that's stuck with me.