Might be unlikely but not impossible - after all if people cared about not breaking existing software Wayland itself wouldn't exist in the first place :-P Xorg

Might be unlikely but not impossible - after all if people cared about not breaking existing software Wayland itself wouldn't exist in the first place :-P Xorg is open source and drivers can be fixed as long as there are enough people to notice and care. Worst case you can run an X root window on top of Wayland compositor and pretend the latter is just a graphics driver :-P.