To be fair, X11 sans extensions is stable, but those extensions are how they provide a lot of the more complicated functionality that's been built since X11 was

To be fair, X11 sans extensions is stable, but those extensions are how they provide a lot of the more complicated functionality that's been built since X11 was born. Wayland originated, AIUI, because we've got layers upon layers of complexity and indirection to bend X11 into what we want on a more recent environment, and building a system with more awareness of what the constraints are in recent systems lets you implement things much more cleanly than those levels of complexity (or, at least, not much worse, if you're using XWayland). (Of course, it's not implausible that in 20 years or less, we'll think of Wayland as requiring lots of kludges and hacks to do what we need then, but you can only plan for known knowns and known unknowns.)