Multiple X sessions (one for each monitor + one for each vnc session + virtual X sessions for whatever reason) has to be combined with Xinemera and with graphic drives and with a KDE/Gnome desktop environment... and all the parts have to fit together perfectly for the system to work. I just don't see that happening anytime soon.
The whole concept of X clients and X servers... it's just too much. X was created back in the 80s, and it still doesn't get the basic usecases right. The requirements for desktop computers have shifted a lot in the last 30 years, so this kind of thing is to be expected.
Starting over every 30 years? I think that's reasonable, especially when it's holding Linux back. We've learned a lot since, and X isn't going to last until 2030... so why not throw it out now?