I played with this decades ago (maybe another Emacs based WM?). It was fun for a while but I moved on. I thought it was abandoned.
I will need to give it another go and glad to see it back among the living :)
The other emacs-based WM I'm aware of is stumpwm: https://github.com/stumpwm/stumpwm
...which is not Emacs based but written in Common Lisp. It is equally hackable, though.