Please, please stop referring to the 6D as the "FF Rebel", even if this is what Canon intends it to be! I would like not to have the "Rebel" name dragged in the dirt, for the Rebel series is one of the most successful DSLR lines a camera building company ever had. It was a Rebel (350D) which brought me to digital reflex bodies and I remember that I had to yearn for almost a year until I could afford it. And this WAS NOT because it was overpriced, but because I could barely afford it back then. Which is not what happens now with the 6D.
It was the very same Rebel which brought me to improving my shooting skills, so much that I clearly understood that improvement would not require a newer body, but a better lens lineup. THAT was the future move to make, and I was happy I made it! This is why I kept shooting my 350D Rebel for 6 and a half years, without even changing the battery, for the original one was and still is good for use!! And when I bought my first and second L glasses I still shot them on the 350D, until had the opportunity to upgrade to the body I was hoping to get. I really doubt someone will ever will say the same in 6 years from now, about the 6D.
It was the L lens lineup which brought me to immediately upgrading this year to 5D3. Yes, I also felt deceived by the fact that the Nikon D800 was a different beast and was upset that I will spend 500 USD more than on the competitor's body, still I never had the remorse for that money, because the 5D3 is (at least for my criteria) the camera I was expecting to get. This sadly cannot be told about the 6D. Paired with my L glasses, the 5D3 delivers as required, the only failure factor being at the moment the person holding the gear.
I stare at this 6D, read the specs and simply cannot believe my eyes. It's like picturing myself in a dream, staying in front of the Canon people and asking them: "OK, so what did you do with that 500 USD extra me and other photographers were willing to pay for my 5D3?" And they pull out the 6D out of a drawer and throw it in my face like a rock!