For those interested in more details surrounding the X Input 2.0 extension, Peter Hutterer has written at length about this input extension update. Peter, of course, is the mastermind of MPX and is the one largely responsible for X Input 2.0. In XI2 Recipes, Part 1, Peter discusses the changes in X Input 2, MPX in XI2, X Input 2 initialization, and other attributes. This is a good read for anyone interested in the input side of X.Org.
Both MPX and X Input 2.0 will officially be introduced with X.Org 7.5 / X Server 1.7. The latest release plans place X.Org 7.5 on the table for a final release in August.