Even if 90% of us don't need X11 for legacy software. It will still be here.

I most agree with you. The Xlibre project may become popular and do something to make X11 popular again. Who knows?

And I just argued on a forum yesterday that Xorg will keep working for 20 years at least. But a lot of smart people claimed I was wrong about it being able to support new hardware. But I think Xorg is likely to build and run for decades yet.

But the X server implementation that is likely to last the longest is Xwayland. And with Wayback, the “stand-alone” X server that many distros will bundle will be Xwayland running on Wayback (Wayland) and not Xorg.

As I have said elsewhere though, few people will be daily driving an X server (Xorg, Xlibre, or Wayback) simply because many desirable applications will require Wayland.

And what will be the x11 only applications that will make people run an X server to use them? Xeyes? Xfig?

I think even running Xwayland will be pretty niche. X11 is going to be a software preservation project. You can boot up OpenLook, CDE, Trinity, or i3 for the memories (and then go back to Wayland for the apps you need).

I could be wrong. Time will tell. Within a couple of years after the release of GTK5 at the latest, we will know. By 2030 maybe.