> I'm not switching to Wayland until my window manager supports it.

Looking at your github, it seems you use StumpWM. It seems they are also working on a wayland version under the name Mahogany. Development seems pretty active: https://github.com/stumpwm/mahogany

> I'll probably switch, grudgingly, to XWayland whenever X gets removed from Debian.

FWIW I think "wayback" is the project for this. It seems to be trying to use XWayland to run full X11 desktop environments on top of Wayland: https://gitlab.freedesktop.org/wayback/wayback