I disagree with the memory card issue "preventing" an upgrade. SD cards are very cheap. As for durability, if you're the average careful person an SD card will survive longer than your camera shutter. Big step backwards in AF? For who? I came from a 7D, why don't I feel crippled with my wife's 6D or my 9 point AF bodies shooting moving subjects? Oh. because the difference in AF is actually marginal with the need for better ISO performance outweighing the need for that said marginal AF performance. You can jack up the shutter speed on the 6D a bit higher than the 7D and get similar results if you've warmed up enough to how the points work in your camera. And you'll still get a better looking set of images in the end, especially indoors or when the sun falls at a game. But no, not everyone shoots sports, sorry.
You can´t upgrade from the 7D to the 6D because you waste a lot of money for new SD cards.
It´s a shame that Canon don´t put a cf/sd card slot in the 6D that the people can change.
The 6D has better image quality, but the AF system and speed is s big step backwards if you come from the 7D.
I recommend to wait for the 7D Mark II (70D) or what the name will be. I hope that the camera will have a CF card slot because I want the camera as a TC replacement.