In reality you don't need all the plate and shit and the retension spring in the middle to design a binding that will latteraly from the heel. You dont need the entire heel piece to move either. Something like a hybrid toepiece with a ramped stepin system that splits the two "heel" wings apart to allow your boot to enter would work just as well. That said, it would take a burly ass spring to even come close to the retension setting you would need to keep a larger skiier in.
Oh, and the line binding is the most progressive thing in the ski industry since elan did the parabolic ski thing, which obviously was just as much of a bad desicsion as line sticking behind these bindings.