I think this is the right decision by KDE. Narrowing the scope of work is basically always a good thing for a project. KDE should either switch to wayland, or stay on X11, and not try to do both. And they've clearly decided awhile ago that they consider wayland a requirement.
I say that despite the fact that I think wayland was a poorly conceived, designed, implemented, and marketed project that has set back the adoption of the linux desktop by years.