As was originally discussed at the Ubuntu 12.04 Developer Summit, X.Org Server 1.12 isn't being called into play for this next Ubuntu Long-Term Support release, but instead they are going with X.Org Server 1.11 while back-porting some of the changes from 1.12 to their 1.11 base.
In particular, the big item they'll be pulling back into their 1.11 xorg-server for Precise is X Input 2.2 / multi-touch. For a few releases now Ubuntu has been carrying their own experimental patches for providing multi-touch capabilities, but now they'll drop their own patch and replace it with the upstream solution.
No other comments have been made about any other changes they intend to make to their 1.11 server stack. Hopefully they will end up carrying the recently published GLX_ARB_create_context patches since that's needed for more modern OpenGL support and with Ubuntu 12.04 LTS being supported on the desktop for a period of five years, that's kind of important.
Sadly, there isn't yet any RandR 1.4 support in the X Server for per-CRTC pixmaps or making it easier for NVIDIA's binary blob to support versions 1.2+ of the Resize and Rotate extension.
Canonical isn't going for X.Org Server 1.12 over fear of potentially new bugs in the LTS cycle and that the binary graphics drivers might not be ready in time. However, NVIDIA is always quick at supporting new kernel / X.Org Server releases. AMD is still generally tardy in introducing new kernel/xorg-server compatibility, but they have been improving their game and in the end they always get out new Catalyst Linux releases in time for each Ubuntu final release. There also isn't any exciting video-related changes in the 1.12 cycle to cause major breakage and headaches for the binary blobs.
In switching from their prototype multi-touch implementation to the upstream-backported patch-set for Xi2/MT, the only fallout they believe is limited to qt4-x11, which will just require an updated Qt4 package with a new multi-touch patch. "Ubuntu has had multitouch support in our X server since 11.04, but it was a prototype implementation. The protocol specification and implementation merged upstream is very similar, but includes a few key modifications."
The new Ubuntu 12.04 X packages are temporarily living in x-testing within the ubuntu-x-swat PPA repository, but will soon be pushed to the mainline Precise repository.
In terms of the rest of the Ubuntu 12.04 X/graphics stack, this next release will begin with the Linux 3.2 kernel, Mesa 7.12/8.0, and the usual updated DDX drivers.
Due to now being supported on the desktop for five years, they will be updating the stack at each point release for supporting new hardware. This will be done by back-porting packages from newer Ubuntu releases back to the Precise Pangolin. Details are in this article.
As a bonus, Ubuntu 12.04 LTS might offer a Wayland Display Server preview, but it won't play anything in the way of an official role until a later Ubuntu Linux release once it has matured.