The latest feature added to Ubuntu's Mir display server is nested rendering support when using Android.
Outside of Android, Mir has already supported nested rendering to effectively have Mir running on Mir going back some time
. Now with Mir Revision 1056
as committed this morning, the necessary changes have been made to its Android platform support to support Mir-on-Mir rendering for Ubuntu Touch.
Nested Mir support is needed to run a Mir session inside the Unity System Compositor.