#1: GRENADE LAUNCHER SAFETY MECHANISM.
Grenades fired from grenade launchers should not explode unless they fly a couple of meters. This will sovle majority of the problems reported with AI noob tube spamming.
#2: CANCELLING SUPPORT.
Many times now in co-op games I've called support on OUR positions, because I wanted to call radio to me not realizing he was already next to me. There's no way to cancel support once called and that's pretty bad.
#3: CALLING SUPPORT FROM MAP.
Not only is it more realistic, it's more convenient and would allow for an easy possibility of controlling the direction of support like the strafing runs which are long enough to possibly clip friendly positions or completely wipe the friendly team out - all due to random direction.
#4: MUCH FASTER SPAWN ANIMATION.
Instead of a long reloading animation, which can occasionally put players at spawn at a ridiculous disadvantage when faced by spawn-killing AI in co-op games, it should just be a quick and flashy cycling of the guns action.