I don't think we'll ever get into that situation. Mir is gone now and Arcan is a pretty niche solution, so I think that Wayland will continue replacing X.org unabated now.
Happy to see Ubuntu make the switch, it'll pull in a good number of daily users and we can iron out the last few remaining issues.
Frankly, Wayland has been excellent to me. It's hard to describe how nice it is that I can't remember the last time I had to open an xorg conf file to try to get monitors working, or get even basic functionality from my touchpad.
Oh, I totally agree—Sway is my favorite window manager on Linux by far. systemd and Wayland and other similar projects are controversial, but they're making huge improvements in the Linux desktop space and the lack of fragmentation is refreshing.
https://github.com/letoram/arcan