two things to say to this:
OP: there sorta is already wreckage when a plane is shot down. only when you shoot off a piece of the airplane, though. when it explodes, theres a few pieces of flaming something that flies away from the big explosion.
2:
Wouldn't having the wreckage of all the tanks and aircraft hang out on the battlefield of X amount of time also tax the servers and pc's that much more?
maybe an option to turn that off? or at least turn it down, like the viewing of ground scenery, from .5 to 4?