I was recently reading Christian F.K. Schaller's On the Road to Fedora Workstation 31 (via both Fedora Planet and Planet Gnome). In it, Schaller says in one section (about Gnome and their move to fully work on Wayland):

Once we are done with this we expect X.org to go into hard maintenance mode fairly quickly. The reality is that X.org is basically maintained by us and thus once we stop paying attention to it there is unlikely to be any major new releases coming out and there might even be some bitrot setting in over time. We will keep an eye on it as we will want to ensure X.org stays supportable until the end of the RHEL8 lifecycle at a minimum, but let this be a friendly notice for everyone who rely the work we do maintaining the Linux graphics stack, get onto Wayland, that is where the future is.

I have no idea how true this is about X.org X server maintenance, either now or in the future, but I definitely think it's a sign that developers have started saying this. If Gnome developers feel that X.org is going to be in hard maintenance mode almost immediately, they're probably pretty likely to also put the Gnome code that deals with X into hard maintenance mode. And public Gnome statements about this (and public action or lack of it) provide implicit support for KDE and any other desktop to move in this direction if they want to (and probably create some pressure to do so). I've known that Wayland was the future for some time, but I would still like it to not arrive any time soon.

(I'm quite attached to my window manager, and it is very much X only. I am not holding my breath for anything very much like it, especially not as far as something like FvwmIconMan.)

Gnome's view especially matters here because of GTK, which is used as a foundation by a number of important desktop programs such as Firefox (but not Chrome, which apparently has its own toolkit system). If X support decays in GTK, a lot of programs will start being affected, and I don't know how receptive the Gnome developers would be to fixes if they consider X support to be in hard maintenance mode.

(But a lot of this is worries, rather than anything concrete.)

PS: I have no idea what non-Linux Unixes are going to do here, especially for NVidia hardware where driver support is already lacking and often at the mercy of NVidia's corporate priorities and indifference.