LLMs didn’t exist when Wayland was started.

Now that we have them, would it be feasible to use LLMs to go after the historical crud that X11 accumulated due to age?

I don’t like vibe coding, but using LLMs to dig into a huge legacy code base like X11 could be very useful.

No.

X11's problems were rooted in the abstractions presented by the X11 core protocol and its extension mechanisms. The interface, not merely the implementation.

Wayland was correct in first focusing on replacing this interface. The problem is the effort stopped there and left the ecosystem to figure out the implementation part.