One of the major features that was going to make up X Server 1.6 was Multi-Pointer X, which had entered the mainline X Server back in May and allows for multiple input devices. This afternoon though it's been stated by Peter Hutterer that MPX won't appear in this next release.
In addition, X Input 2 also won't be ready for X Server 1.6. In place of X Input 2 in the 1.6 server release will be X Input 1.5 with device properties, which landed into git master after the X Server 1.5 / X.Org 7.4 release.
Peter's confirmation of no X Input 2 / MPX can be found on the X.Org mailing list. What will be ready for X Server 1.6 is Predictable Pointer Acceleration, Direct Rendering Infrastructure 2, and RandR 1.3.
If the X.Org development community can stick to a release schedule, X.Org 7.5 and X Server 1.7 should be out in April. If the X Input 2 and Multi-Pointer X code has matured enough, we'll finally see that input hotness in Q2'09.