Ah, fvwm. Now thats an old war horse of a window manager. And it is still maintained no less.

I do wonder if anything Wayland related will have such staying power.

It's indeed actively maintained!... lots of changes and updates recently. They're cleaning up the code base. After using it for over 12 years, I'm still amazed just how incredibly flexible fvwm is. You can even mimic tiling with a bit of effort (see here: https://www.youtube.com/watch?v=xdSgf-IykIo ).