So I been thinking... Would it be better to actually earn certs/xp for a class AS you play the class? Also, how about the same idea applied to using the vehicles? This would encourage people to actually USE what they want to BE rather then just, say, go MAX or get in a tank and go on a killing spree to level up another class that they haven't yet played yet want to level up (HE rounds were nerfed for a reason folks).
Of course, once you got the max stats on a unit that might cause some problems. So perhaps a better idea is not to simply only gain certs/xp for the class but to have bonus certs/xp for the class you're playing.
That then leaves us with the issue of people wanting to level up all the classes instead of actually sticking to a class they'd like though. this might need some thinking on. So start thinking already!