Yes, there is already the Xorg state tracker in Mesa for providing 2D EXA acceleration along with X-Video acceleration, but this new XA state tracker hopes to eventually replace this older state tracker for X acceleration purposes.
VMware developed this new state tracker (and they also wrote the Xorg state tracker too) as part of overhauling their virtual graphics driver. The Xorg state tracker would not die, but would be re-tooled back to a module configuration to handle a generic "xf86-video-modesetting" DDX.
VMware developed this new state tracker, which is also based upon the Xorg state tracker acceleration code, but to better deal with versioning between the different X/Mesa/KMS interfaces. So what's new to this XA state tracker is versioning support, surface functionality (allows for a basic DRI2 implementation), and YUV blits for textured X-Video. Also planned is X Render compositing support, solid fills with ROP functionality, and copies with ROP functionality and format conversion and re-interpretation.
Obviously, VMware designed this XA state tracker for use by the "vmwgfx" on their VMware-virtualized guest operating systems. Thanks, however, to the Gallium3D driver architecture, this state tracker can be adapted to support the other Intel, ATI/AMD, and NVIDIA drivers too.
More information can be found in the XA state tracker announcement by Thomas Hellstrom. For now this state tracker is living in the xa_branch of Mesa, so it will not likely be merged prior to the Mesa 7.11 release next month.