I'm not sure I like this idea... hear me out...
I haven't been playing battlefield for long but I've found that the squad mentality is very important... so instead of having people focus on a class, we should try to focus on designing squads for different objectives (defending/attacking with vehicles, mowing down infantry, rushing, defending an area... etc), and have people that are able to play as at 1-2 classes effectively adjust to what is needed from them at the moment in order to complete a squad that's trying to accomplish a certain goal
I gave some examples of squads in the strategy section... they could definitely use some work... but it's a start
for example... as far as mowing down infantry: 2 assaults with 2 medics can do a lot of damage