This code has not yet landed in the mainline code-bases of the X Server, libXi, inputproto, or xinput, so for now he has this working implementation running in his own Git repositories. Peter though has re-based this work off the latest X.Org Git code and "it works without issues" while implementing the X Input 2.0 draft specification. While X Input 2 is working, there are currently a number of limitations and there are several features still missing.
In Peter's mailing list are all of the details along with how interested parties can help out and where X Input 2.0 is going to go. What is not clear at this point, however, is whether this revised input extension will be ready for X Server 1.7 / X.Org 7.5.