I think if you give every soldier some sort of C4 explosive then it'll make the veichle usage much more interesting since you can't just rush in with your tank otherwise someone will just run at you and chuck down some C4 (although I guess people will be moving slower so you might need to remove any rapid fire weapons from within the tank).
Something that might be cool is electrical sensors which sense electrical activity, i.e electrical weapons, other sensors and other suits. Players could shud down their suit akin to Shattered Horizon. You could have a whole host of sensors such as infra-red, nightvision and movement-vision (plus aforementioned electrical sensor) but you could limit to one-type per person or make them expemsive so that teams have to co-ordinate and share information. There could also be things to block individual sensors such as cold-blooded thermal camoflage.
Something that would also be nice is a UAV which instead of showing as dots on the map comes up as a toggle-able display on each players HUD of the camera from the UAV piloted by a member of the team.
My last idea is more of a pet-peeve than anything which is the ability to choose what kind of sight to use (Modern Warfare 2 sort of got this right with the RDS and the holo sight) but I'd like to see even more options. A good attachment system would be brill too (although it wouldn't neccesarily be good for this game).
EDIT: How many shots should each person take before they die?