A year and a half ago, shortly after the GNOME 45 release, I opened a pair of Pull Requests to deprecate and remove the X11 Session. A lot has happened since. The GNOME 48 release addressed all the remaining blocking issues, mainly accessibility regressions, but it was too late in the development cycle to drop...
GDM won’t be able to launch X11 environments after GNOME 50 is my understanding.