Speaking of infinite ammo... the map that comes to mind that would be really changed by it is Walls. A handful of infantry could basically hold the top forever and gunners/rocket soldiers could blast buildings indefinitely. Granted that already happens with vehicles, but it's harder to go all the way up there and kill the gunners/rocket soldiers, as they can hide in the little rooms up there. That would really be my only concern with infinite ammo. I'm down for trying it out this week/weekend.
Infinite ammo mutators already exist, just nobody uses them anymore.