The video market is in the process of being merged with the still market however. That started with products like the 5D series, and now camcorder options are becoming fewer and fewer as the need for a specialist camera like that declines.
The market progression will be towards systems like the 70D. Cameras like the 70D and the GH3 were the first real steps towards systems dedicated to holistic image capture rather than the old fashioned specialists. I doubt that any high end camera released from now on from Canon/Sony/Panasonic is going to be a specialist, they will have to be able to perform both functions at the highest level. Obviously Nikon are not seeing it that way, based on their latest camera, they are going the way of dodo. Of all of the major camera companies, they are the ones who really don't get it (either that, or they lack the resources to adjust to the new reality).
New versions of the 5D, 6D and 7D will be expected to reflect the state of the art, and in the context of their video capabilities that will mean 4K.
The 7D was originally rumoured to be released in 2013, but it did not show up. Instead, the 70D was released. IMO there was a management decision based on how the overall market was developing that resulted in the insides of the original 7D2 prototypes being repackaged as the 70D, and the 7D2 went back into development to capture the sort of capabilities that would allow it to be competitive through 2017. If it did not have 4K capabilities it would be obsolete as far as video is concerned long before then.
Your logic makes sense, but that said...it kind of assumes 4K content is going to be widely used and distributed by everyone very soon. I'm not sure it works like that. Look at what happened to "3D". Are we all having conference calls via our smartphones in 3D now? Are we all taking stills images in "3D" now?
I appreciate the higher quality 4K allows, don't get me wrong. It's lovely to watch. However, nobody with a 50 or 60 inch tv can even see all the detail if they sit farther away than 6 or 7 feet. Last time I checked, most people have their tv in a living room or family room where it sits on one wall, they sit near or against the other, and the young kids sit (or play) on the floor in the middle.
So I kind of see "consumer demand" for 4K content, falling very flat within 2 years after it becomes mainstream. Why? Well, because history has shown that people want convenient low quality video to play on smartphones (if at all...they mostly like to play games)...rather than high quality video that can only be appreciated on a large screen. Also consider just how much more memory and bandwidth it consumes.
Is there a coming revolution where everyone is going to buy a $1000+ "prosumer" DSLR (where before they only bought a consumer video camera), just to shoot a few home videos, and then a 50 inch 4k monitor to watch it on? And that's going to be a boon to the electronics industry? I think not...
Sure, the next gen xD DSLR's might feature 4K capability. But is Canon going to rush them to market just because Sony and Panasonic bring out some compact cameras that can do it?
What will Black Magic's reply to all this be? 6k or 8k at $4k? Do you know how large of a screen you would need to make use of that resolution? How about 160 inches diagonal...