[md8z]

All of that is extremely possible with a web app though, and most of it is probably done even easier with a web app. In fact that is the usual way to build a web app, make a server that does the heavy lifting and then make a GUI that runs in the client which can then be accessed by multiple users. You can easily access them from a smartphone too.

The only exception is this:

"Another case might be several users running on one machine each with their own displays and inputs."

This would be multi-seat which doesn't really have anything to do with the display server. It is implemented in udev and logind, which spawns additional X or Wayland servers for each additional "seat".

[ddingus]

Seems you highlighted the differences nicely enough.

[md8z]

Is that sarcasm? A key difference I would say is that the web is actually better because you can run javascript or WASM code in the browser, in X that would be the equivalent of the "server"...

[ddingus]

Not at all.