Sam Spilsbury, the former Canonical employee and Compiz developer, has been working on XBMC porting as part of this year's Google Summer of Code.
The code was cleaned-up to make it less X.Org dependent and Sam ended up getting XBMC running on Wayland. After getting the HTPC software running on Wayland, he then decided to try to get it up and running on Mir.
Sam Spilsbury wrote today in a new blog post, it's now up and running. "As part of my GSoC project to make XBMC work on newer linux display systems, I also wrote a backend to make it render on the Mir display server too. This was actually quite straightforward, and took about the same amount of time to get to same point of completeness as it did for Wayland support. There’s no mouse or keyboard input support yet, but only because I haven’t had the time to implement it yet. Should be done in a few days."
His Mir code for XBMC can be found in this GitHub repository.
Canonical's Oliver Ries confirmed on Google+ that this is the first "Mir client out in the wild", i.e. not dependent upon XMir.