Canonical is making its own display server for Ubuntu, called Mir. The Ubuntu developers are also working on the next iteration of Unity, which is at the moment available only on the mobile platform, but it seems that it's now a lot closer to being integrated successfully on the desktop.
The Ubuntu developers have been accused of fragmenting the community with their Mir display server, but they continued their work uninterrupted. They initially planned to release Mir in Ubuntu 14.04 LTS (Trusty Tahr), but that plan fell through when they realized they were not going to be ready in time.
Moreover, the current development cycle has been focused more on the mobile version, on the “old” Unity7, and on providing the best Ubuntu LTS version possible. The developers didn't stop improving Mir, which is after all the default display server on mobiles, but the desktop version will not feature it yet.
Ubuntu 14.04 LTS users have been able to try for some time a technical preview of Unity8 and Mir, which can be selected from the LightDM greeter before logging in the operating system. Before the current updates, you could only see a small window with not much to do in it, but now more improvements have been released for the Unity8 session, including a hardware mouse.
As it stands right now, users will be able to get a much better look at how Unity8 looks and works on Ubuntu 14.04 LTS and it might get even better after more updates are released. The developers also showed another very interesting aspect.
After logging into the Unity8 session, which is running under Mir, they opened a guest X11 session and the transition seems to be rather smooth. The technology is still young and clearly many things can be improved, but the desktop looked awesome and different.
And this is where Ubuntu developers will have to be very careful. When they decided to release Unity and replace the aging GNOME2 desktop environments, the community didn't react too well.
The Unity8 desktop environment looks great, but it doesn't feel at home on the desktop and is very different from Unity7. There doesn't seem to be a desktop, just the Unity interface, and we can only hope that the desktop version will provide a proper experience in the future.
In any case, users don't have to worry about Mir arriving too soon to replace X as default, but it's good to see that great progress is being made on the Unity8 and Mir front. If Canonical pulls it off, Unity8 will be one of the most interesting desktop environments out there.