Wayland (the protocol) supports the necessary bits and it's up to the compositors if they want to go the extra mile to support everything.
My own personal take is that most compositors won't because X does not represent multi user graphical computing in the way that most people use it today. That role is fulfilled by web applications.
We may find or choose for that to not be a thing.
Ok, fine.
The X window people did make that a thing and the end result is powerful and flexible.
None of that makes efforts like Wayland bad. They aren't.
But they, by your own definition, are a subset of what X is too. They aren't thinking it through, by design. That is OK.