Sony recently announced the new A7S, designed for 4K video.
There is a lot of discussion about 4K and whether it will take off or fail like 3D TV. To be honest for content providers there is a case for going to 4K, while consumers are yet to take up 4K it does make sense for film makers to produce their content now in 4K ready for the future.
Putting 4K in what are predominately still cameras to me makes less sense. If your going to shoot movies then use the right equipment. By the time you have purchased all the accessories to make it work you might as well have bought a proper video camera and now 4K video cameras are more available.
There is a case for video in still cameras but its mainly for news paper photographers, they need quick short clips, sound bites for websites. The rest of us also might want to pop a quick short clip onto our websites or YouTube but if your serious about moving making then buy a proper video camera for that use.