MEH... Will we VS get a massive plasma accelerator (Better Lancer) for our Infiltrator/Heavy? If so, SURE
This idea has been brought up before. The most interesting version I heard was a rifle that can disable certain parts of the vehicle with targeted shots. For example, you could hamper its movement by shooting at the treads, maybe you could blind the driver by shooting at the camera on the turret. An engineer could repair this damage, of course. A straight-up vehicle-destroying rifle would be very difficult to balance. If you had any chance to kill a tank by yourself with this rifle, then a handful of infiltrators could practically instagib tanks by focus-firing them from the rear. It's pretty much like the VS Lancer, except infiltrators could easily sneak behind the armor column and strike without warning. As for a vehicle-damaging sidearm, the crossbow with explosive bolts already exists, so I guess you could take that as a baseline for AV pistol balance. The railgun version would have to do less damage, thanks to its higher velocity, but the explosive bolts do almost negligible damage already and are only really good for kill stealing.
Not every class should have a tool against the enemy in every situation. That would just make the whole concept to have classes specialized in certain areas obsolete. So, no. Infiltrators should not have any tools against vehicles. Furthest I would go, would be the ability to hack the terminals on deployed enemy sunderers.
