Taken in a vaccuum, I certainly see the argument for height/weight.
But with a change like this I'd be EXTREMELY worried about unintended consequences. I can easily see trying to make a move with this and screwing up five other things.
There are still going to be very, very few players who would be capable of playing that far out of position (i.e. guard at center, etc), so I see any potential issues here as minor and rare.
My preference would be to have defense split into perimeter and interior capabilities, although I don't know if that would be difficult from a programming standpoint or not.
(And remember, height and weight are already built into the ratings.)