For users of older window managers on newer distros where X is likely to be removed "soon-ish" (vs LTS distros), the answer just to use Wayback. It is a different X11 server implementation that uses Wayland under the hood, and is enough to run your WM. There are already people who use it to run AwesomeWM, IceWM, etc:
https://gitlab.freedesktop.org/wayback/wayback