Or perhaps by then we will have moved onto another protocol that's even simpler.
Better idea: fix the bad life choices that got us to this point, so we don't have to keep re-living them. What a concept!
I think we would all love it if we could magically fix every bug or design flaw in existence with a wave of the hand, unfortunately in real life it takes time and experience to do things right.
It doesn't seem surprising to me. As X.org has gained extensions over the last 30 years, toolkits that speak X11 find themselves having to decide which extensions they'd like to use. Adding flexibility on this naturally leads to a bigger feature matrix. Of course, the toolkits are also free to drop support for X servers that don't have those extensions, which in turn would shrink the X11 backend.
I have no doubt that in 30 years, they'll have a similarly-sized feature matrix for all the Wayland extensions they'll want to support.