Hello,
I kinda see how this could help, but it would need to be better understood first before being applied (it would need, of course, to not link directly to GL and use function pointers :-) ).
Heck, it should make performance almost worse as we add a round-trip to the X server to do this and need to flush the GL rendering pipeline at each buffer swap instead of continuing sending commands to display the new frame while the swap occurs...
I am not a GL expert, but AFAIK the OpenGL spec requires the app to flush the rendering pipeline before swapping the buffers. Many games don't do so(ut, Q3 & friends, Half-Life, ...) Most drivers are prepared for this, so it doesn't make any problems. It's only the fglrx driver that can't cope with it, and it makes the mouse pointer lagging for up to one secound, which makes FPS games unplayable.
The best solution would be to fix the games, maybe ATI could fix their driver, but so far there are only hacks like my patch or a preloaded library with a custom glXSwapBuffers.
Stefan