Ring ring, ring ring
ssh -X, ssh -Y, and Xpra work just as well on Wayland as they do on X11, thanks to the magic of XWayland currently being a required component of both GNOME's and KDE's Wayland sessions. Not to mention that there are Wayland versions of RDP/VNC clients. TeamViewer also has support for remoting into a Wayland session, and both KDE and Gnome have/are about to release off-by-default support for RDP-ing into a running Wayland KDE/Gnome session.
You're cheating, your solutions all use X or full desktop sharing!
You never specified I couldn't, the requirement was "run GUI apps remotely on a local Wayland session", and you very much can! 0:)
But they're gonna take that compatibility away because they're all against me and good ol' technologies! What then?
Can't comment on the second half, but yes, X11 compatibility is more likely than not going away in an unspecified time frame (there are -- pre-release? -- versions of at least one of GNOME/Mutter or GTK that can be built without X11/XWayland support). If/when that happens, there is waypipe. It's not the be-all end-all user experience (uncanny-valley invocation compared to ssh -X, noticeable more jank than Xpra -- still largely[1] within the same ballpark) and it requires installing it on the remote end (like Xpra), but it has similar performance to Xpra (both waypipe and Xpra are much kinder than ssh -X on bandwidth, almost on par with RDP/TeamViewer/etc).
PD: I get legitimate gripes with the current state of Wayland/Wayland app support (accessibility and Chromium-adjacent software not enabling their existing Wayland support by default being the more salient ones), I get "as it is I can't use this", I even "get" not liking change, but at least come at Wayland with actual, legitimate gripes. What I don't get (or at least, find extremely self-conceited) is "I refuse to adapt to anything new", and "I will stay with (blah), and the whole world shall keep maintaining it in production-ready until I get bored with it", for any value of (blah). Personally, the two big blockers I encounter in my own tech bubble are:
- Flickering XWayland windows on KDE when using Nvidia graphics cards (solved in Plasma 6.1 + Nvidia driver 555 series and up, but those are not yet available on Ubuntu)
- No support in AnyDesk for remoting into a Wayland session
The first one doesn't affect me (I don't own/regularly use a PC with Nvidia graphics), the second one only affects me in the PC my parents use, and even then I haven't had to AnyDesk into it in years now.
[1]: Unlike Xpra, it exposes you to this issue if running GTK4/Gnome applications from a KDE local endpoint (with the workaround being to install icon packs on the remote end).