From the article entitled “Mir Devs Are Still Working On An Example Mir Desktop Session For Ubuntu 18.04” posted on Phoronix:
[The example Mir desktop session] could just be a basic MirAL / Mir Kiosk example or other very basic example akin to Wayland’s Weston compositor. There’s also been some speculation in the community that Canonical is working on getting the GNOME desktop stack working with their Mir Wayland compositor for some more magnificent goals down the road.
In the comments section, the lead developer for Mir acknowledged that Ubuntu 18.04 will likely ship with an example Mir desktop session, but didn’t provide many additional details.
I would post a link to the article, but unfortunately, links to Phoronix are banned on the /r/linux subreddit.