Peter Hutterer announced on the X.Org development list early this morning that X Input 2.0 will be pulled into the X Server master branch a week from today, on the 4th of June. While this input code is finally hitting the master code-base, the API or ABI is not finalized yet and is subject to change in the coming weeks. Peter also shared that X Input 2.0 is quite simple while the next version of Xi, X Input 2.1, will be more feature-complete.
Some of the features of X Input 2.0 include sub-pixel precision for coordinates, 32-bit keycodes, maniulation of the device hierarchy, support for multiple pointers (MPX), and simplified event selection. X Input 2.0 will hopefully officially make it out with X Server 1.7 in X.Org 7.5 this August.