DRI3 (also known as DRI3000) will be present in Mesa 10.0, which is likely to be released before the end of November. See the earlier Phoronix articles if you're not yet up to speed on Direct Rendering Infrastructure 3 and the new Present Extension for X.Org. In several of the late Thursday commits, DRI3 support was added.
On the server side, X.Org Server 1.15 will support DRI3 and it's expected to be released as stable around the end of the calendar year. Right now though the main driver just fully taking advantage of the new DRI3 capabilities is the open-source Intel Linux GPU driver as DRI3 and the Present Extension were spearheaded by Keith Packard and Eric Anholt of the company. DRI3 was just conceived last year at XDC2012 but it's made a lot of headway and will be a nice X.Org improvement while many users are holding out for Wayland or Mir to take over on the Linux display server front.