Agreed with bombastic bob but with less all caps.
Wayland is STILL not feature-complete -- it's an ongoing issue of "What about x, y, an z?" "Oh, why would you want to do that?" I recall years back Wayland didn't suport multiple monitors, reporting fresh rate, or syncing stuff to refresh rate... and yes, there was even the response "Multiple monitors? Why would you want that?" (Personally, I don't have enough problem with tearing to care about sync to refresh but those that do care do care.) Current day, there's a battle between security (you don't want some random app to be able to take screen grabs and take over keyboard and mouse) and functionality (you want a remote desktop app to do exactly that.... so last I heard, the response was "Why would you want to do that?" and a bunch of twiddling thumbs). And sure, you may not want to run programs over the network, but from time to time I do, it would be great if they could at least come up with a "use compisiting to draw into an off-screen window and send differences from one 'frame' to the next over the network" type of solution for this, but the answer is generally "Well, why would you want to do that?" In addition, benchmark-wise (last I saw one), Wayland was not running any faster than X11 and in some cases was slower.
That said -- I do kind of view Wayland as a solution looking for a problem; but, Wayland has slowly gained features (as they realize "Oh why would you want to do that?" will not fly and even if reluctantly implement the missing functionality.) I expect eventually Wayland will be feature-complete (it's much closer now than it was years ago), I have no reason to not use it at that point, and I do appreciate that Wayland is cleaner from an aesthetic standpoint and jettisons numerous amounts of X11 functionality that were already irrelevant in a modern system 20 years ago yet alone now.
As for GTK5 dropping X11 support -- well, I was going to argue that's unlikely based on the large number of backends gtk has, but I guess that was gtk2 or gtk3 -- actually GTK4 is down to Wayland, X11, Win32, Mac, and Broadway (which I've never heard of but essentially uses HTML5 and web sockets to allow a GTK app to display in a browser, although I'm not sure what the details are on this at all.)