The Intel/Marvell 2700 has a MBX lite 3D accel., and has (or had) extensive looking documentation on how to use the chip. Could this be of help?

The Dell Axim x50v and x51v had this chip with an OpenGL ES driver for Windows Mobile. There is a port of Quake III: Arena that was playable at 640x480 on the x50v/x51v. I'm guessing it'd be a good target for reverse engineering drivers, if MBX and MBX lite are fully compatible. There are even dual frame buffers if you want to play around with redirecting the 3D output (one framebuffer on the processor SoC, one on the 2700G). Unfortunately, the Linux port for the X50v is not very far along last I checked.