Originally Posted by TFL Replica
No need to panic yet.
That mostly reads as "you're on your own if you don't get with our program". Any one of a dozen major distros offer much better support for X11 and will continue to offer good support for X11 after wayland becomes mainstream as wayland has made specific allowances for X11 and it's developers (who also work on X11) plan on supporting X11 for a long time to come as primary support software.
Originally Posted by cdoublejj
Is MIR a GUI?
Mir (like X11 and wayland) is the platform that the GUI runs on top of.
As to the problems with X11 and how Wayland wants to solve them (and a couple comments on Mir), check out this article by one of the wayland developers (also an X developer)