Did you check this:
Also if I remember correctly there are some problems with current Mir on desktops which should be resolved in next version 0.1.6.NOTE: You may need to undo the damage done when libhybris was installed by running the command
sudo update-alternatives --config x86_64-linux-gnu_egl_conf
and choosing the non-libhybris alternative. The symptom that you need to do this is an error in /var/log/lightdm/unity-system-compositor.log that says something like this:
undefined symbol: _glapi_tls_Dispatch
There are a couple of bugs, one in Mir and one in QtUbuntu, that can cause Unity8 to fail to start. Fixes for these are working their way through the system. You will see errors in the file ~/.cache/upstart/unity8.log.
You may also run into trouble if you're using the proprietary drivers for your video card.
When I installed the unity8-desktop-session-mir in daily live image of Trusty and run the update-alternatives command libhybris was default.
Unity8 session on Mir didn't work for me I ended up with black screen. Most likely it was the Mir bug.
ok... it is indeed very easy to install simply install the unity8-desktop-session-x11 or -mir package and off you go. the only thing that held me off is that i couldnt find to switch sessions on the login screen. (clicking on the ubuntu logo next to the username...)
however the mir version delivers a black screen and the x11 version is hardly usable and not really for dekstop but an android simulation (looks like one: small vertical screen and scrolling through unity scopes left and right when you manage to click the left menu on the clock screen)
to go back just switch to console and type "unity" to get your desktop and change session back.