@winterschon Thanks a lot for the offer, I'll most likely get back to that, but it might take a while (it feels like I'm 80% there, but OTOH, a lot of building blocks are still missing, like e.g. menus and tooltips, have to see how to handle them correctly, as they must be "transient" windows without decorations and with specific behavior ...)
Regarding #wayland, my feeling is quite similar: Sure there are issues with #X11, but wayland didn't really convince me it's "the solution". I always prefer non-disruptive, evolutionary improvements, something that's in my experience prevalent in #BSD systems (while the #Linux ecosystem loves to reinvent the wheel and break everything every other day, to exaggerate a bit 🙈)
Maybe an #X12 could indeed be the better solution. Take it with a grain of salt, as I really have no "inside" experience with X, but "drop all stuff nobody uses any more and at the same time declare *some* extensions mandatory" would look pretty great to me ...