The biggest thing I can think of is that X11 is more flexible when it comes to specifying custom resolutions; which some people use to output 240p on CRT TVs for emulation. AFAIK, there is currently no real equivalent for xrandr on any Wayland compositor.
I’ve also noticed that Grsync’s password prompt is broken on Wayland. Thankfully, it has a feature that lets you preview the command it’s about to run, so that you can copy and paste it into a terminal.
Being a KDE user on EndeavourOS, I use Wayland everyday. I switched over a few years ago for Waydroid, but now X11 isn’t even an option for me with the current release of KDE.
Switched my HTPC from a regular Debian desktop with X11 to Plasma Bigscreen (Fedora) with Wayland. Biggest frustration I have is Kodi can’t automatically adjust the TV’s fps, but besides that it’s been going smooth. Steam Link even works well for streaming games from my PC!
Vibe coded a Kodi addon that actually changes the fps, but if anyone knows an actual solution that’d probably be better.