I predict there will be a systemd-style debate about removing X11 by 2030 and it will be completely gone by 2040 (since someone mentioned 20 years). There won't be a single non-composited OS available at all and people born after 2000 won't really remember anything else.

There are still distributions that do not use systemd though, e.g. two that come to my mind are Slackware if you are more conservative or Void if you prefer a rolling distro.

And TBH IMO the choice of window system affects way more the day-to-day operations of a desktop oriented distribution than the init system ever did, so i expect slightly more friction about removing Xorg (as a sidenote the server is Xorg, X11 is the protocol and another server - most likely a fork of Xorg - can continue providing it if Xorg shuts down).