Linux

I admit I may misunderstand the situation; I hear there's a compatibility layer or something named xwayland -- will that allow older apps linked against x11 to run on a wayland desktop?

Yeah though older apps on Linux are always a bit sketchy. "We don't do that here" is kind of a thing... Most stuff is at least regularly rebuilt.

It's also kind of a weird comparability layer... Like it works really well, but basically they run an X server in the background, and then just paint the windows on the X server to your Wayland desktop and map all the clicks back.

So... X apps get a real X server to run on and then rest of your apps run natively in Wayland which provides a lot of benefits.

In any case, Wayland fixes some stuff it provides more than feature parity. A big one for me is KDE has a composited and non-composited mode on X and they actually have different behaviors. If you launch a game it automatically goes to non-composited mode because how compositors work on X is kind of a mess and it introduces latency that people don't want in their games. On Wayland it's always composited mode but it's designed for that, so you don't have the drawbacks in terms of performance. So... You can play a game without your desktop suddenly functioning differently and without sacrificing performance in the game.