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.
X will however stay for the next release, Ubuntu 11.04, though and possible some more releases after that. As Shuttleworth mentioned, six month is an unrealistic period for something like this. We may see some signs of Wayland in Ubuntu in about a year (Ubuntu 11.10). However moving the entire ecosystem to Wayland will take several years.
Wonder if LM will continue with Ubuntu 11.10