Canonical is working on the next iteration of Unity, and the Ubuntu developers have implemented a large number of changes for it and for the Mir display server.
The new Unity8 desktop environment developed by Canonical is only working on the Mir display server, so a lot of the fixes affect both components. Ubuntu developers have been making great progress on Unity8, although that progress can only be visible on the Touch platform.
Both Mir and Unity8 will have to wait a little until they are ready for the Ubuntu desktop. According to the latest information about this subject, the Mir display server will probably be available by default in Ubuntu 16.04 LTS, the next long-term support iteration.
On the other hand, Unity8 is a little closer to a desktop release, although it will not be ready in time for the Ubuntu 14.04 LTS release, which is expected to arrive on April 17. Users will be able to test a technical preview, but a full feature version might be featured in Ubuntu 14.10, in a little over six months.
The reason why Unity8 is all that important is that it represents one of the most visible pillars in the convergence project initiated by Canonical. The developers want to have a single code base for the desktop and and Touch version, and Unity8 is probably one of the most visible components.
Kevin Gunn, the leader of the Mir and Unity8 project at Canonical, has shared some information about the progress made by the Ubuntu developers.
According to the changelog, for Unity8, new scopes have been added in silo and design-approved (they will land in the next Ubuntu Touch promotable image), a new icon theme called Suru will be implemented soon, the transition to Qt 5.2.1 has been finished, the split greeter has received a number of improvements, the Notifications and the Greeter have been refined, and the developers are preparing to implement autopkgtests (QML UI tests and autopilot integration tests).
The Mir development team has been equally busy. For example, Mir has been updated to version 0.1.7, a key bug fix has been implemented for a crash that happened on login for the Unity8 desktop preview, the work towards providing cursor support for Unity8 desktop preview is still in progress, a number of screencasting improvements have been added, some shell authorization capability has been implemented, and the developers are working to improve the compositor/gl render split interfaces.
If you want to see Mir and Unity8 in action, just install the latest version of Ubuntu Touch on a Nexus 4 or Nexus 7 device.