Pretty simple concept I thought of.
When you kill a vehicle within (X amount of time from the driver bailing out) you receive 100 points (point value is for example only).
If you kill a vehicle with the person still in it, it's 100 points.
How does this solve the issue? Easy, whether the person is in it or if they bail out, you still get the same reward. That way, you aren't pissed when he jumps out last minute. The only thing you'd be missing out on is the killspam.
Now, if you want to kill the guy who bailed for the extra infantry kill exp, you can. But it isn't necessary to get your full amount.
If you don't understand my ramblings, just say so
Edit: Just to add, from what I've seen thus far it looks like the kill exp system is similar to BF3. You blow up a vehicle, you get something like 100 xp. You blow up a vehicle with someone still in it, you get 100 xp for the vehicle destroy plus the points for killing the person inside.
This is different from my version because whether or not the guy is in the vehicle, you still get the same amount of points. Obviously, if the guy hasn't been in the vehicle for 30 seconds or something you want get the full xp and you'd just get the vehicle destroy amount (or none at all).