The Xubuntu team had been contemplating using XMir for their Xfce Ubuntu distribution with the 13.10 October release, up to and including putting out XMir Xubuntu development images. However, after collecting extensive feedback from those comparing XMir to a pure X.Org Server, they have decided to not yet adopt any Mir technologies.
Xubuntu 13.10 would have been using XMir as the X11 transition layer to running a rootless X.Org Server on Mir since the Xfce desktop is written in GTK2 (and being ported to GTK3 for Xfce 4.11 and future updates), which doesn't yet have a native Mir back-end and other changes for supporting Mir. As testing has revealed, there's a big performance penalty to using XMir at this time.
At today's Xubuntu meeting, they decided to not use XMir for Xubuntu 13.10 as shown by the meeting minutes. They also rejected the notion of waiting until the Ubuntu 13.10 feature freeze to decide on the Mir/XMir state after the remaining features have been added. As a result, Xubuntu 13.10 will be running a straight-up X.Org Server.
More good news from this Xubuntu meeting is that they agreed to cherry-pick Xfce 4.11's xfce4-settings and xfdesktop improvements into Xubuntu 13.10. Xfce 4.11 was supposed to be released earlier in the year but it has yet to happen. However, Xubuntu developers will be trying to pull in some of this new code into Xubuntu 13.10 for the benefit of end-users.