There's definitely pluses over the 5D2.

-- Size, some maybe argue they want the bigger body but DSLRs are big as it is and the smaller size of 6D can be a plus for some. Plus the body still has a substantial portion that is magnesium alloy.
-- SD card is actually a plus for non-7D upgraders because we already have SD cards. CF cards would be another investment.
-- Modern design
-- Reported low light capability
-- Improved ISO performance that appears equal to 5D3.
-- Silent shutter option
-- Some may have no use for WIFI, GPS but I'm sure many people will take advantage of those

There's a large portion of people who flat out just can't afford a 5D Mark III. Once the 6D price is reduced to $1500 - $1750 I think it will open possibilities to more people. I know I couldn't look my wife in the face if I dropped $3,000 on a 5D3.

Dave