Last week there was some surprise that the new Intel 3.0 Linux DDX driver would feature integrated support for XMir. There's small work needed to the DDX X.Org graphics drivers to be able to support running XMir, similar to XWayland for Wayland users. The support was merged as Canonical said the XMir API should be stable. In releasing a new 3.0 xf86-video-intel driver snapshot, Intel's Chris Wilson wrote in a Git commit that Chipzilla will not carry XMir patches upstream.
Intel has heavily invested in Wayland and has many full-time employees working on the competing display server. It now doesn't want any XMir support in their mainline driver. However the U-Turn from Intel comes just days after it was committed and to publicly state a neutral stance on Canonical's controversial display server. Now Canonical will need to carry the XMir support out-of-tree from the xf86-video-intel driver.
Canonical is carrying patched versions of Mesa, xf86-video-ati, and xf86-video-nouveau for being able to support Mir/XMir in Ubuntu 13.10. Binary AMD and NVIDIA graphics drivers also remain incompatible with Mir.