I don't get why you'd think this has anything to do with desktop. Not only it doesn't have X or Wayland, but it also doesn't allow multitasking.

You'd be much better off with Neo900/Pyra or even SailfishOS (Jolla) once XWayland is ported (I think that all works except for touch input for now).

EDIT: I'm not even sure if Ubuntu Touch uses Mir - last time I checked, it used Android's compositor SurfaceFlinger, but this news is almost 2 years old, so it might have changed.