How many times is this? It seems like Canonical enjoys rebuilding Unity every Ubuntu release. It seems there's plans afoot to replace X.org with a homebrew solution called Mir.
Mir's initial code is now available for tinkering but it's really early days and isn't something anyone would want, or be able to, use on a daily basis. Far from it. This is just an announcement of Canonical's plans (for Ubuntu 14.04?).
So... first we get Unity on Mutter. Then, the moved to Compiz with a Unity 2D on Qt. Then Unity 2D got scraped. Then, there were plans to use Wayland in place of X.org. And now we're getting a new display server replacement and Unity will be rebuilt using Qt/QML running on top of this new unknown server.
Why do I get the feeling we won't be seeing Mir for very long?