So far as I can tell, the arguments for replacing #X11 by #Wayland are :
→ X11 is old, and computer programmers are compulsive novelty–seekers who burn down their own homes every 2—3 years on average
→ X11 does not support a small number of exotic use cases, which could reasonably be handled by specialized software
→ X11 has numerous sets of extensions which all do pretty much the same thing in subtly different ways