Inspired by his first experience with the 5K Red Epic, Vincent Laforet somewhat recently addressed this sort of topic. http://blog.vincentlaforet.com/2011/06/07/what-camera-did-i-use-to-make-this-still-picture/
I think stills from high-resolution video might replace traditional stills cameras within limited segments--i.e. event or sports photographers would certainly find applications. And if the Cinema DSLR is going to hit 4K MJPEG at 24 frames per second, I think that relatively (that is, relative to a car) affordable cameras with high-res/ high-fps capacity will test the market in the near future.
That said, for many photography applications, it makes more sense to retain discrete modes for both stills and video-- and I don't think that will change any time soon. I also don't think that the high frame rates will translate to the high, high megapixel scene as quickly as it will to the 4K/ 5K market. That is, I doubt we're going to see a 5D mk V (or whatever the 2020 high MP Canon camera is) that fires off 45 MP frames at 60 per second-- let alone sustained speeds of that kind. This sort of speed is even more unlikely in the legitimate medium format realm. More likely, we might see bursts of 20-30 frames per second at relatively high MP counts-- but not the prolonged video recording that would legitimately replace, say, the fashion photographers camera. I haven't even addressed big segments, such as landscape photographers, that won't give a lick about this sort of advancements. So in many senses, I think many popular aspects of stills photography are pretty well insulated against cinema encroachment.