DRI3 is expected to be one of the (hopeful) major features alongside the X.Org Server GLX Rewrite for X.Org Server 1.15 when it's to be released around year's end.
This first major update to the Direct Rendering Infrastructure since DRI2 seeks to make it possible to share DMA buffers as X pixmaps, share synchronization objects, and provide assurances of accessing the correct DRM device.
Of the DRI3 work over the past year, finished are the X protocol extensions, the DRI3 XCB bindings, a Mesa DRI3 loader, the GLX API support for DRI3, the X.Org Server changes, and the changes to the Intel Mesa driver and xf86-video-intel DDX.
Still to be accomplished for DRI3 is coming up with an EGL API, the X.Org Server GL loader for DRI3 drivers, and ideally support by a non-Intel driver to ensure things work well for Nouveau or Radeon too. The work to date has been mostly done by Keith Packard and obviously focused around Intel Linux graphics driver support.
For those X developers that weren't at the X.Org Developers' Conference this week in Portland and would like more information on the current DRI3 undertaking, see Keith's PDF slides.