X Server 1.8 was a success in terms of getting more patch review done and getting the release out (nearly) on time for once, so X Server 1.9 will follow much the same process. However, Keith has called for a few more changes with X Server 1.9.
In preparation of the X.Org graphics drivers moving back into the X.Org Server at some point (likely X Server 1.10 or later), Keith will first be merging all of the X.Org protocol headers into a single repository. This should happen in the coming days so that all of these source header files can be obtained from a single, central location.
Also with the hopes of moving the graphics drivers back into the X.Org Server -- something that Luc Verhaegen is in stiff opposition to -- the X.Org Server release process may be even shorter. Keith is calling now for a three month or so release cycle. This is in contrast to X Server 1.8 that was done on a six month release schedule, but for older releases we have seen that stretch out much further.
Quicker releases of the X.Org Server would be needed to deliver new hardware support and other changes since the X.Org graphics drivers would no longer release updates individually. Daniel Stone has already publicly questioned what about delivering such driver updates in X.Org Server point releases rather than new full-blown server versions, but this has yet to be discussed on the mailing list.
For the first even shorter release schedule, Keith Packard is calling for X Server 1.9 to be released in August. Releasing in August would allow time for X Server 1.9 to make it into Fedora 14, Ubuntu 10.10, and a later release of MeeGo, for which Keith is now interested in as well due to Intel's involvement.
This 1.9 release schedule that was published today would result in the merge window closing on the 1st of June, a non-critical bug deadline going into effect on the 1st of August, and the official X Server 1.9 release to come on the 20th of August. There would also be snapshots / release candidates in between those targeted milestones.
Packard's X.Org Server 1.9 thoughts can be read on the xorg-devel mailing list. As of right now there isn't too much discussion surrounding these proposed changes.
Nothing too exciting is planned for integration with X Server 1.9 besides maybe seeing XKB2 finally.