I have a 5D mk2 and I am definitely not considering getting a 6D. I am sure there will be improvements over the mk 2 but I doubt the improvements would validate an update.
Only body purchase I might consider is the high mp one if it has good DR... I am mainly shooting landscapes, so don't have much of a need for high fps or AF system a la 5D mk3 or 1Dx.
6D is an entry level FF though, I do not think it is aimed at anyone who already has a FF camera...
I would get the 6D over the 5Dm2 (I think). I will need to see more details. The GPS is a major plus for me with the photos I shoot. And I hope Canon gets in the habit of adding built-in GPS now.
But, that 45MP, High Dynamic Range camera is still the future...