I suspect several people may already have mentioned this, but one thing I noticed dabbling in the WoW stress test is that when I played with a Warrior my first thought was "Hey, maybe *this* is how Tankers should work!"
Basically, Warriors special abilities don't use "endurance" as in other games, they use "rage", and rage starts at zero and goes up as you get hit. So it's not specifically that the warrior gets more powerful the more damage he takes, but it basically fuels his ability to use his powers.
I suspect it may be just too divergent a mechanic to be worked into CoH, and I certainly haven't played with it long term to know if it has other complications, but it's an intriguing idea. (To me, at least.)
