[Cloudef]

It already exists and its called xwayland. Most wayland compositors also have X11 WM inside them...

[Izkata]

You misunderstand: I'm not talking about the X protocol, I'm talking about some new all Wayland thing just so window managers can be separated from the other things you'd otherwise have to implement.

[Cloudef]

Yes and ironically Xwayland is that, but you probably want something like Arcan

[pantalaimon]

I think Mir can do that