When you think about it, the new Combiner that has Optimus, Prowl and Rodimus in it would have to be the most conflicted Combiner - the leg, torso and chestplate would all think that they should be the one in control of the gestalt - they'd be constantly telling other parts of the body to shut up! Might as well have a combiner made of Megatron, Starscream and Shockwave

Would make Menasor look downright sane