Bryce Harrington, Canonical's principal X leader, has shared his views about the X.Org package set for Ubuntu 10.04. As far as the X Server goes, Bryce believes it is a question between the 1.6, 1.7, and 1.8 releases. X Server 1.7 has been shipping as part of X.Org 7.5 since early October, but Bryce is still willing to consider using 1.6 in Lucid as an option since it's been tested longer than 1.7. However, X Server 1.6 lacks support for X Input 2.0 / Multi-Pointer X, VGA arbitration, EXA improvements, and many other goodies. Using X Server 1.6 though would likely just be a fall-back scenario if going with X Server 1.7/1.8 does not work in Ubuntu's favor.
Meanwhile, X Server 1.8 is scheduled to be released in March as the inaugural X.Org release under a new development process. X Server 1.8 is set to include XKB2 and other new features.
At this point it's looking like the X Server that will end up in Ubuntu 10.04 LTS is X Server 1.7.x (likely a 1.7.2 or 1.7.3 release). With Ubuntu 10.04 being a Long-Term Support release by Canonical, Bryce is looking to be conservative with Lucid and ensuring there is a stable X Stack in this release. There will also need to be proprietary graphics driver support in Ubuntu 10.04 by the time it ships in April, which would give AMD only one shot (Catalyst 10.4) at delivering X Server 1.8 support, seeing as they tend to not focus on supporting new kernel/X.Org releases until they are officially out. NVIDIA though should have support for any X Server 1.8 changes in the driver this year or in early 2010.
When it comes to the Mesa 3D stack for Ubuntu 10.04, the likely version will end up being Mesa 7.7. This version is set to be released by Christmas, which also gives plenty of time for the Mesa 7.7.1 stable point release before April. Mesa 7.7 was branched just this week and carries numerous Gallium3D improvements, GLSL improvements, support for some new OpenGL extensions, and various other work. The Mesa stack in Ubuntu 10.04 LTS should also provide "out of the box" support for ATI Radeon R600/700 series graphics.
For the Intel graphics driver there will likely be the Intel 2009-04 or 2010-01 package set, but this may be influenced by what kernel ends up getting into Ubuntu 10.04. If only the Linux 2.6.32 kernel makes it in Ubuntu 10.04, using the Intel driver stack from Q1'2010 may not be possible due to DRM changes.
Personally we would really love to see Ubuntu 10.04 LTS shipping with X Server 1.8 and the Linux 2.6.33 kernel, but with this being a Long-Term Support release and all, we will be likely let down. Getting in the Linux 2.6.33 kernel would mean support for new hardware and plenty of other kernel changes, but for X.Org it would mean the new VMware kernel driver that's needed by their virtual Gallium3D driver that was just introduced, the KMS page-flipping ioctl that would allow more Ubuntu users to play with Wayland, various graphics DRM updates, and potentially even basic mode-setting/2D support on the ATI side for the Radeon HD 5000 series.
Right now this is all up in the air but we will see what ends up getting settled for Ubuntu 10.04 LTS and we'll certainly be around with our benchmarks when the time comes.