Ubuntu’s Mir display server may not be default on desktop until 2016
It has been almost exactly one year since Canonical announced Mir, a replacement for the X window system. Mir was originally planned to become the default system in the Ubuntu desktop for the 13.10 (October 2013) or 14.04 (April 2014) releases, but it was delayed due to compatibility problems in multi-monitor setups. Those problems were with XMir, an X11 compatibility layer that ensures that Mir can work with existing applications built for X.
It made sense to not turn Mir on by default in the upcoming Ubuntu 14.04 because that's a Long Term Support release that must be stable for five years. But instead of saying that he intends to flip the switch later this year or in 2015, Canonical founder Mark Shuttleworth this week said he expects to do that by the 16.04 release in April 2016. Shuttleworth's comments don't necessarily rule out turning Mir on by default before 16.04, but it's not something Shuttleworth is ready to promise.