The Ubuntu GNOME developers have confirmed that, for the time being, their distribution will continue to use X, at least for the Ubuntu 14.04 LTS cycle, but they might switch to Wayland sometime in the future.
The entire Mir versus Wayland issue has been dividing the communities, but Ubuntu GNOME users shouldn’t worry too much, at least not yet. Even if GNOME devs are betting their money on Wayland, that particular implementation is still far into the future.
“Ubuntu 14.04 is using X and it is not going to just disappear overnight! Ubuntu GNOME 14.10 will likely continue using X, even if Ubuntu switch to MIR. At some point in the distant future we will probably switch to Wayland, but right now it’s not even close to being ready,” said the developers.
It's going to be very interesting to see what the solution for this problem will be once Canonical adopts Mir, but developers have at least a year before having to worry about this issue.