The unthinkable is becoming closer to reality it seems. The idea of AMD working hand in hand with little to no issue with a companion Nvidia GPU has come to light with the recent press release from LucidLogix. More info explains:
http://www.sempercog.com/?p=1494
It looks like all of the AMD HD 6950 cards appear to be ready for unlocking, at least for now. According to Wizzard from Techpowerup, it is a matter of a simple BIOS flash and your HD 6950 can easily turn to an HD 6970. AMD even made the process a bit easier as AMD included the dual-BIOS feature...