The primary target of xf86-video-intel 2.18 is to address outstanding bugs. The bugs namely addressed are changes for limiting the maximum object size, incorrect clipping of polygons, limiting the number of VMA cached, and latency in processing user-input during continuous rendering.
The Glamor acceleration architecture support is also integrated into xf86-video-intel 2.18, but it's disabled by default and still requires various changes to your stack outside of the Intel DDX.
The Sandy Bridge New Acceleration (SNA) is also still inside and represents a majority of the changes to xf86-video-intel 2.18. Chris Wilson has an amazing 678 commits to the xf86-video-intel 2.18.0 release, most of which were around improving SNA. See the latest SNA benchmarks and information in this article.
The xf86-video-intel 2.18.0 release announcement by Chris Wilson can be read on the mailing list.
In terms of what Intel's doing next, read/watch Intel's Brewing New Linux Graphics Driver Features.