Here are my thoughts:
1. Neither the 6D nor the D600 is impressive enough to make someone switch camps IMHO.
2. I think the the 7D mII will be focused on speed like the current model is. I'm guessing dual Digic 5+, better AF with more cross type points, and 10 FPS. Also, Better high speed video.
I would be suprised if they increase video FPS honestly, but it would be nice. I also think it could be more expensive than the 6D.
I would be seriously suprised if it did, the reason FF costs so much more is because the sensor costs a lot more to produce. The 7D II will almost cerntainly cost less than the 6D. I think the 7D and the 6D are going after different photographers.
3. I also think we could see the end of the xxD series and have a high level rebel take it's place and the EOS-M take the place of the low level rebels, but we will see.
The Rebel type line won't be discontinued because they need a cheap lineup for people who don't want or need anything better (right now that is ). The EOS-M is not a replacement for the Rebel line but a new niche for Canon, people who want something more like a PS but with great IQ.
Lastly, I think that the photographer is evolving. Cameras in phones are killing point-n-shoots, mirrorless will be purchased instead of entry level DSLRs, and that leaves only the series photographers to by the "expensive" cameras. There will be room left for a fully spec'ed rebel (like the T4i), an entry level FF (like the 6D), and entry level speed demon (like the 7D), a full featured FF (like the 5D mIII), and the ultimate Pro focused on speed (like the IDX).
There is a niche for everything and right now they are filling in segments for photographers and not shifting up or down segments.
I may be totally off, but there are my predictions. Don't flame me too bad
OK, I will just broil you....