You can run applications over the network with (edit: waypipe, not pipewire, I mix up the names every time), which works quite well. Technically it's not "transparent", but it isn't on X either because pretty much 0 UIs today draw themselves using X11 primitives, they just draw their own buffer and get X to display it.

This isn't really an answer to your question, but under Gnone3+Wayland "ssh -X" works as you might expect. Which amazed me at first, because I wasn't expecting it.

Turns out it's because most applications are X11, Wayland supports X11 applications via XWayland, and X is doing network transparency like it always does.

I don't think network transparency is a goal for Wayland. X11 network transparency was awesome in the late 80s and early 90s. In many universities, there would be rooms of X11 terminals that connected to the "big machines" in the server rooms- and you could have each of your applications, even even the window manager itself, all being run on different machines.

This made sense when an institution would license software for their big iron, and when desktop computers weren't nearly as powerful as they eventually became during the 90s.

But most people gave up on it right around the time that Netscape Navigator, with its very bitmap-heavy UI gained traction. The X protocol really wasn't designed around this. Extensions helped, but not enough.

I bet the vast majority of people using X11 today have never run a remote X11 client.