Re: NVidia and XRandR 1.2
The nouveau driver now has full RandR 1.2 support for all GPU types except NV5x (IE. 8000 and 9000 series cards) and even that support is partly working. It appears to have had extensive testing on NV4x GPUs.
Both the Radeon and RadeonHD drivers now support RandR 1.2 So counting the Intel driver all of the major open source drivers now support RandR 1.2. It is only the proprietary drivers that are lagging so far behind.