For xeyes that works. It is absolutely an inferior and chatty protocol for any other application though, like try to watch a youtube video in chrome through it.
X's network transparency was made at a time when we drawn two lines as UI, and for that it works very well. But today even your Todo app has a bunch of icons that are just bitmaps to X, and we can transfer those via much better means (that should probably not be baked into a display protocol).
I think Wayland did the correct decision here. Just be a display protocol that knows about buffers and that's it.
User space can then just transport buffers in any way they seem fit.
Also, another interesting note, the original X network transparency's modern analogue might very well be the web, if you look at it squinted. And quite a few programs just simply expose a localhost port to avoid the "native GUI" issue wholesale.