The first xf86-video-intel 3.0 development release came a half-year ago with the big feature being SNA acceleration by default. Initially the big driver update also carried XMir support, but Intel ended up backing out that XMir patch due to a decision by Intel management and reported XMir performance issues. Intel is also heavily invested in Wayland.
Later updates to the xf86-video-intel 3.0 code-base have yielded a better tear-free experience, stability fixes, Broadwell support, and many other changes.
This new version, xf86-video-intel 2.99.911, is still introducing new functionality. This time around the Intel X.Org driver picks up work for allowing the X.Org Server to work with Intel hardware without needing root privileges when used in conjunction with systemd/logind and the updated DDX drivers. The changes involve server-side file descriptors and a backlight helper to use the RandR backlight property without needing root privileges.
The xf86-video-intel 2.99.911 driver additionally has various bug-fixes. More information on the changes for this latest xf86-video-intel 3.0 snapshot can be found via the Git change-log.