@IceWolf In fairness, the WM + display server can be separated in Wayland. There's nothing intrinsic to wayland to prevent that.
Wayland is just a protocol, not an application. It's down to the compositor implementor's decision whether the WM and display server run as separate process. It just happens to be simpler to implement them together.
@IceWolf The trouble there is that you now have to decide on a protocol that those WM's speak with the display server, and then need to get people to implement it.