You're forgetting that capturing a photo vs. recording a video are two different things. From what I've read on the Black Magic's 4k camera, it can only record video. Sure, you can pull a still frame from a video clip but the shutter speed, aperture, and ISO settings will be far more limited compared to simply capturing a photo to begin with. Example, video recorded at 24 fps cannot have a shutter speed slower than 1/24, thereby eliminating the possibility of capturing a longer exposure.
DSLRs, mirrorless cameras, and many compact cameras have had the ability to capture a photo or record a video for years now. The limitation I stated above is the very reason why the two will naturally remain two distinct activities. Yes, there will be overlap such as time lapse photography converted to video or pulling a still frame from a video clip, but only working within the confines within this overlap will prove to be very limiting.