It started out as a discussion earlier in the week whether all of this old code should be dropped from Mesa, but developers were overwhelmingly in support of the efforts. There was just one or two developers against the move, and then concerns by some in the BSD-land for their sad state of graphics drivers that hoped to see Matrox and Voodoo GPU support kept around. Oracle didn't care too much about graphics drivers for Solaris.
The drivers/hardware that no longer have mainline Mesa driver support are listed below.
i810: Early Intel 8xx series IGPs
Mach64: ATI Mach GPUs
MGA: Matrox GPUs
r128: ATI Rage 128 GPUs like the Rage Fury, XPERT 99, and XPERT 128
Savage: S3 Savage GPUs
SiS: Crusty SiS GPUs
Tdfx: 3dfx Voodoo graphics cards
Unichrome: VIA IGPs (Well, the ones where there was actually support available.)
Dropping the DRI1 drivers listed above eliminated over 85,000 lines of code from the Mesa tree. Code that was mostly unmaintained and didn't receive new feature support work in years.
Also being executed last night was the linux-fbdev software driver and the gldirect and ICD drivers for Microsoft Windows. This work took lightened the Mesa code-base by another ~37,000 lines of code.
Next on the Mesa chopping block was BeOS operating system support, but that was just around 2,000 lines of code in Mesa.
The Mesa code-base was trimmed up by over 100,000 lines of code in an effort to modernize the stack and reduce the maintenance burden for Mesa/X.Org developers.
The commits are in Mesa Git master and the first release to go without these drivers will be Mesa 7.12 when released in January. This release may also be tagged as Mesa 8.0, if the OpenGL 3.0 / GLSL 1.30 support is finished by the end of the year. Mesa 7.11 series is the last for those with the vintage graphics hardware.
Regardless of the hardware in use, be sure to participate in the 2011 Linux Graphics Survey.