At some point there probably will be some incompatibility. They will learn from experience and might find a big change is necessary.

I hope that they would take a stepping stone approach. If they tweak the screen size then you could replace the top lid, screen, etc without replacing the bottom.

Perhaps when a motherboard redesign is required they launch the new version whilst keeping the old for a couple more generations to help transition.

Change will be necessary at some point. Hopefully they make it as pain free as possible.