In Plasma 6.8, there will be no X11 session in the login screen. There will only be a Wayland session available to log into.
In 6.8, all X11-specific code paths in Plasma for Plasma Shell, System Settings, and device configuration will be gone.
This means that the next distribution releases (Fedora 45, Ubuntu 26.10, and Debian 14 in 2027) will ship KDE plasma with only Wayland.
Our internal metrics within KDE show that over 95% of users of Plasma 6.6 are on Wayland, with a gradual increase every release. The metrics also show that basically no one is testing or developing Plasma on X11 anymore. The platform was already, for all intents and purposes, abandoned by KDE contributors.
This number is most likely sampled by the opt-in telemetry and crash reporting diagnostics. So it could not include those on older plasma releases with X11 or have switched to another desktop for X11.
What do you think? GNOME has already removed X11 from GNOME 50 this year and now KDE is following not that far behind. 
Like someone else has commented, the main thing that seems missing that is important is accessibility. Apparently people that need screen readers or other aids are just hosed as I understand it.
It might be a chicken-and-egg situation though, where nobody focuses on Wayland in this area as X11 is familiar and (still) working, so more display managers moving over might also eventually shift the (probably very limited) Dev resources over. At least I hope so.
Screen readers have been solved for a while via OrCA's updates which cover gtk+ and qt applications under wayland, though all of linux really needs better accessibility to compete in that arena. That being said yes as the zeitgeist essentially forces developers off of x11 more will take their knowledge to wayland which will even further speed up the (unfortunately) niche areas of development that might be missed.
There's also government funding for accessibility improvements in linux (like the Newton project from the German government) which should help solve several of the challenges.