Pointer Barrier Events of Xi 2.3 make it where if a pointer hits one of these defined barriers, events are sent to selected clients. Via Barrier Release Requests, a client can "release" the pointer so that it can pass through the barrier with the next movement. The use-cases for Pointer Barrier Events is hot-corners/edges that respond to pushing against them (stemming from GNOME 3.x developer requests) and ad-hoc transparent barriers so depending upon the pointer speed the user can move the barrier (a request by Ubuntu's Unity developers).
Current issues with this work come down to grab behavior being different for other events, loss of Predictable Pointer Acceleration across a barrier, device-specific release isn't yet implemented, and a passive grab test is currently failing.
Aside from touching the X.Org Server, updating to X Input 2.3 also requires changes to inputproto, libXi, and the xorg-integration-tests.
Hutterer ends his mailing list post with "I think this is a valuable addition to 1.14, unless someone can find significant issues with the protocol as it is proposed here. Should we merge this for 1.14, I do reserve the right to disable this feature in the server before the release, unless we have a credible client-side implementation. We've learned the lesson with smooth scrolling that a server-implementation only is not good enough."