Does anyone remember MPX? It was a set of patches on top of X11 that let two people use one computer at the same time. Two mouse pointers for two mice, and two keyboards for input. It was super fun in a dorm environment (I was at Random hall at the time) to browse the Internet with friends. I wonder what it works take to revive it for Wayland.
It's part of XInput 2.0 and works as well as it ever did with upstream X.org. The more popular approach to multiseating these days involves logind, udev and two video cards (or drm-lease-manager). Then the two display servers are completely independent from each other, which may or may not be what you want.