I agree disagree with those who say why does Canon not just keep selling a 5 year old body? Because would you buy a 5 year old BMW when Mercedes is selling new cars for the same price? Sure both are nice cars, but there have been improvements over the last 5 years. I could almost promise that the 6D will be better than a 5D2 in every way. Better AF, Better metering, Sensor improvements maybe?, Better LCD, Faster FPS hopefully. Pop up flash.
Actually, if I was in the market for a nice car, but I didn't have the coin for a brand new one, I would probably go for that 5 y/o BMW and be completely content with it. I'll let somebody with a fatter wallet than I get that new Mercedes.
I love my 5DmkII. A replacement FF for ~$2kUSD is going to be something less. Better get your 5DmkII while you still can.