From what I saw on the OpenGL you found the windows links downs.
The windows system and the Mesa system are almost the same. Note the almost the same. Program calls Opengl32 it interfaces with the lower driver.
Microsoft Default Opengl is 1.2 Mesa Opengl Default is something like 1.6.(Heck load more processor load)
Basicly Mesa will need a cut back. So it performs. Mesa default needs a Opengl verison change feature for improved performace in software mode. This could go into the main branch. OSMESA32.DLL Under windows is the default driver for Mesa This can be changed. Compare OSMESA32.DLL to the NVIDIA and ATI you will find there are verry simplar only Minor changes will be required to make them work with MESA in the standard plugin location. Ie the OpenGL plugin system in windows is the OpenGL plugin system. Basicly patch the plugin system.