Canonical planned to make XMir the default display driver for Ubuntu 13.10 (Saucy Salamander), but it seems that they will not be able to fulfill that promise.
Canonical cause quite a ruckus when they announced their intentions to bring XMir as the default choice on Ubuntu 13.10, instead of X. They even seemed pretty confident that they were going to be on time.
According to the developers, Canonical has two clear goals: to ship Mir + XMir + Unity 7 on the desktop for those cards that support it, and fall back to X for those that don’t, and to deliver a native Mir + Unity 8 running on Ubuntu Touch.
While the second goal will be achieved by the time of the launch, shipping XMir on Ubuntu 13.10 (Saucy Salamander) will not happen.
“Mir has made tremendous progress and is currently available on the Ubuntu archive for use, but there are still some outstanding quality issues that we want to resolve before we feel comfortable turning it on by default.”
“Many of these issues live in the XMir part of the stack, which provides the integration between the X server and the underlying Mir system compositor,” reads the announcement posted on the official website.
The problem resides with XMir and its capabilities. Whilst it's able to handle one monitor just fine, the quality of multi-monitor support has been lacking.
“The multi-monitor support in XMir is working, but not to the extend we’d like to see it for all of our users. The core of Mir is working reliable, but with XMir being a key component for our 13.10 goals, we didn’t want to compromise overall Ubuntu quality by shipping it,” is also stated in the announcement.
Users will still be able to install and run XMir, if they chose to do so, from the official repositories, and Canonical has also assured us that the talks with the GPU manufacturers about Mir support are going forward.