The next major transition for Unity will be to deliver it on Wayland, the OpenGL-based display management system. We’d like to embrace Wayland early, as much of the work we’re doing on uTouch and other input systems will be relevant for Wayland and it’s an area we can make a useful contribution to the project.
We’re confident we’ll be able to retain the ability to run X applications in a compatibility mode, so this is not a transition that needs to reset the world of desktop free software. Nor is it a transition everyone needs to make at the same time: for the same reason we’ll keep investing in the 2D experience on Ubuntu despite also believing that Unity, with all its GL dependencies, is the best interface for the desktop. We’ll help GNOME and KDE with the transition, there’s no reason for them not to be there on day one either.