Well kind of. It'll be several decades before we see any practical benefits - at the moment once you have local execution you can do anything you want - accessing other apps or even root is trivial.

Phoenix[0] has some good ideas about how X11 could be made more secure without breaking backwards compatibility. I don't understand what was so fundamentally broken about X11 as a protocol that it required a replacement protocol.

We can argue about limitations of X.org's implementation of the X server, but, as demonstrated by Phoenix, X.org doesn't have to be the only X server implementation.

[0]: https://git.dec05eba.com/phoenix

How do you make a global hotkey in all compositors with Gtk or Qt?

...which is overkill when you only need a Vulkan or GL canvas which spans the windows client area... and even with GTK or Qt your app still stands out like a sore thumb on the "other" desktop environment because the window chrome doesn't match the rest of the system.