I was under the assumption that FF gave better IQ than crop. So even with the new 70D on the horizon wouldn't the 6D be a better choice?
Is the 6D's auto focus as really bad as everyone says?
Modern APS-C sensors have IQ almost as good to FF sensors in good shooting conditions. Its only when you start pushing the ISO up that the differences become more noticeable. In recent years, Canon's APS-C sensors have been lagging a bit compared with the competition, but its widely expected (hoped?) that a generational improvement will come through soon. If that happens, finding differences between a FF camera and an APS-C camera at low ISO's will be tough - if you look very closely you might notice some differences in the shadows or highlights, but otherwise...
FF sensors retain an advantage with shallow depth of field and blurred backgrounds. The cameras with FF sensors are also very feature-packed and well built, but also cost more and tend to be bigger and heavier (6D aside?).
All up, its probably best to conclude that a FF sensor is better, but in many common situations you would be hard pressed to see it.
The pricing on the 6D makes me think new FF cameras are within the financial reach of more people. And as the IQ gap narrows, people will make buying decisions on the features of the camera as a whole (such as high ISO capabilities, AF, weather sealing, viewfinder, FPS, video features etc) without automatically assuming that a FF camera is the be-all and end-all. If the 7Dii has an improved sensor, I'm going to be very curious about how it performs sale-wise compared with the 6D.