Here's a possible differentiation that no one's brought up: video-centric features.
The 70D has the new dual-pixel autofocus during video, and its inherited the All-I recording option found in the current-gen XD full frame cameras. But early sample footage suggests image quality isn't much better than that found in earlier ASP-C Canon models. Lots of artifacts, sub-HD resolution, etc.
That means the 7D II could feature some kind of significant step-up in video features. Maybe it will have a cleaner image, like the 5D Mark III (though I doubt it, if the 7D Mark II shares the 70D's sensor). Or maybe it will be a little sharper, like the 1DX, or even like the 35mm crop mode in the 1D-C. Or maybe Canon will do something really surprising, like implement decent video encoding. The much-ballyhooed All-I recording feature is better than the original implementation, but something that uses 4:2:2 color space would be nice, or that legitimately had a broadcast-ready bit rate.
Much of the problem isn't even the codec they used. You can get 4:2:2 uncompressed over HDMI on the 5D3 now and.... it barely looks better than what the in cam shot footage delivers. But then look at ML RAW and it's holy cow! Sooo much more detail and much better DR and more natural looking noise/'grain' patterns. They are doing something funky in the single chain. Maybe Digic is a crap processor and they are retooling it to do a much better job of debayer, scaling, range compression, etc. Maybe they realize they need to ship all the 7,5,1 series from now on with RAW option too since that also also brings many more bits of depth which does help in ways too. Maybe they need to add 4K option too. And chips fast enough to read the whole sensor at once so non-2x2,3x3 block scaled sensors can be free of moire and aliasing?
Also, Canon is going to have to move the lower-level C-series cameras to 4K relatively soon. Maybe not in the next year, but if the 7D Mark II is a 2014 camera, I wouldn't be surprised if a C300 mark II and a C100 mark II appeared shortly thereafter. If Black Magic ever gets its manufacturing act together, and if Sony keeps pushing hard on price, Canon's hand might be forced even sooner. So I don't think superior video specs on a 7D Mark II will cause any trouble with C-series bodies.
If Canon is smart they will forget worrying about hurting low end C series and losing to BM and perhaps Sony or who knows who else. If the 5D3 had delivered something close to ML RAW quality and usability features from day 1 it may have flown off the shelves and excited the video forums more.
Dual-phase pixel AF is one thing to help a lot but the IQ for video needs to be way fixed up too from the 7D.
And now that people have seen ML RAW.... bar is high.