This latest set of patches is for "feature set 1", which is GPU output slaves. It contains the necessary infrastructure changes with some additional cleansing for allowing additional GPUs to serve as secondary "slaves" to the main GPU via output providers.
There's the GPU provider support, pixmap sharing infrastructure, scanout pixmap support for RandR, platform bus hot-plug support, an autoAddGPU option for the xorg.conf, and more.
The patches begin here on the mailing list.
For additional background information see provider object support for RandR 1.5, yesterday's GPU offloading and USB hot-plugging demos, etc. [Pardon the terse update while on an airplane.]