I'm sure there has already been a thread on this. I just thought I'd throw my idea out there.

All vehicles need some sort of countermeasures module, with flares and a lock detector.
Especially with the new AA HAVs
Any dropship should be able to fend off swarm launchers using flares.
Since swarms already have multiple rounds a pop, the effectiveness of the flares could be dependent on the module level, only stopping a limited number of swarms per usage at lower levels.
This gives vehicles a new skill and equipment based defense.
It will still leave free LAVs vulnerable, and with higher dropship and HAV survivability there will be one more counter to murder taxis.

This changes little for forge gunners, turrets, and av nades, but swarm launchers now have an added challenge. Higher level swarms could have better tracking, as well as power, in order to have slower missile detection by the vehicle. This can be related to their signature, making all new types of AV dropsuit set ups, like stealth AV.

As another bonus for Vehicles, target locking can possibly light up the AV on the map.

These are just a few ideas, that without any solid numbers can't be seen as balanced or not, but it adds a few new Vehicle vs. AV aspects.