A session happened this morning about the Unity8 Desktop Preview Image as a way for early adopters and developers to try out the Unity 8 and Mir stack ported to the desktop on the Ubuntu 14.10 base, while the official Ubuntu 14.10 release image will still be using Unity 7 with the X.Org Server. Those interested in learning more about this image and the plans can find the details via summit.ubuntu.com with the Google Hangout Video plus notes.
Additionally, via Launchpad is the blueprint item. There's also now daily builds of Ubuntu Desktop Next 14.10 with the latest packages of the day. In due time there will also be some early Phoronix tests of this Ubuntu-Desktop-Next spin.