Hello Linux Geeksters. As you may know, Ubuntu 14.04 Trusty Tahr, which is scheduled for release on the 17th of April, will be using an updated version of Unity 7, running over the X.org server, while Ubuntu Touch is powered by Unity 8 running over Mir.
Most likely, Unity 8 will be ported from the mobile version of Ubuntu to the desktop one, for Ubuntu 14.10.
Stephen M. Webb, one of the Ubuntu developers has posted a video of both Unity 8 (Mir) and Unity 7 (X11) running on the same time, in two different sessions:
In the video, Stephen logs onto Unity 8 (over Mir) from the LightDM greeter, opens a guest session with Unity 7 (over X.org) and switches back to Unity 8, showing us that the two can run fine, in parallel.
For now, Unity 8 is very tablet focused, but Canonical will not add it like this, on the future Ubuntu systems.