It was just a few days ago that Unity 8 and Mir updates landed for Ubuntu Phone. The latest round of Mir work for v0.1.6~0.1.7 included screencasting improvements, work towards providing cursor support for the Unity 8 desktop preview, IPC improvements, and other interface enhancements.
In the upstream Mir development repository, Mir 0.1.8 is already being prepared. Among the Mir 0.1.8 work includes a mirserver ABI bump, switching over to udev for device enumeration and hot-plugging, logging support for HWC events, continued consolidation of Mir Surface classes towards a simpler architecture, decorations for the Mir demo-shell, and other improvements. Pushed yesterday was also work on multi-monitor improvements for Mir.
While these updates are coming quick, there's still a lot of heavy-lifting to be done for Mir, particularly when it comes to Mir (and Unity 8) on the desktop with most of the Canonical development focus for the time being is centered around the Ubuntu Phone/Tablet endeavors and its Android base. All we know now is that Mir should be on the Ubuntu desktop in the next two years in an official capacity.
In case you missed it, Canonical posted a new Unity 8 + Mir demo video a few days ago.