With X Server 1.6 being a strictly time-based release cycle, it's unknown whether X Input 2 will be completed in time or if Multi-Pointer X will be enabled by default. We may not end up seeing X Input 2 until X.Org 7.5 / X Server 1.7, which would be well into next year.
While X Input 2 isn't ready yet, Peter Hutterer has back-ported his device properties protocol into the X Input 1.5 extension. Last night on the X.Org mailing list he proposed his patches for the X Server that will remove the Configure/Query property functionality and replace it with his device properties protocol. This work comes in the form of three patches for the X Server plus patches that will be required for the evdev and inputproto support.
This work hasn't yet been merged to git master, but can be found in Peter's mailing list messages. No input API breakage has occurred from this change. For those interested in the specification to the device properties protocol, the first draft of it can be read here (the final version of the documentation will be pushed with the patches).
The good news here is that until X Input 2 is completed, at least we'll have X Input 1.5 with device properties.