The distinction on what went to -lib and what was in the main ext was the accelerated graphics.
Having libGL available with Xvesa is of no use, not even software accel that way. Mplayer-xorg's edge is the GL output, which also requires the Xorg server.
Building Mesa in such a way to work just as libGL, without the GLX extension and the swrast DRI driver, is possible, but has to be done separately. Not worth it IMO, the software renderer is very very slow. (no, a core i7 couldn't do glchess with it over 15fps)
libdmx: only used by the Xdmx server & related
libpciaccess: only used by Xorg & drivers
libdrm, libkms: only used by drivers, Xephyr, libGL
I guess as long as no accelerated graphics are required (which IIRC is the case for some games) just having those "GL" libraries should be sufficient to work with 'Xvesa'.
Please point out a single game that links to GL without needing acceleration
Even if they are sufficiently simple to run on the sw renderer, that isn't available with Xvesa.