Aside from David's DDX driver API re-work and other API/ABI breakage to the xorg-server, David's updating the Resize and Rotate extension to the X.Org Server. He's ultimately hoping to have DRI2 offload slaves and output slaves by this September with X.Org Server 1.13.
His proposed RandR update is to add the concept of "provider objects" to this popular X extension. As said by his mailing list message, "A provider object represents a GPU or virtual device that provides rendering or output services to the X server. This is the first rev of a protocol to enumerate providers devices, set their roles, and provide generic properties based on output properties for them."
This provider object work would form RandR 1.5. Here's some additional details about why you might be interested in provider objects with RandR 1.5:
1.5 Introduction to version 1.5 of the extensionAt this time there's no other planned features to RandR 1.5.
Version 1.5 adds a new object called a provider object. A provider object represents a GPU or virtual device providing services to the X server. Providers have a set of abilities and a set of possible roles.
Provider objects are used to control multi-GPU systems. Provider roles can be dynamically configured to provide support for:
1) Output slaving: plug in a USB device, but have its output rendered using the main GPU. On some dual-GPU laptops, the second GPU isn't connected to the LVDS panel, so we need to use the first GPU as an output slave for the second GPU.
2) DRI2 offload - For dual-GPU laptops, allow DRI2 applications to be run on the second GPU and display on the first GPU.
3) GPU switching - Allow switching between two GPUs as the main screen renderer.
4) multiple GPU rendering - This replaces Xinerama.