It also could be interesting for bird and sports guys - it gives you 30 frames per second (maybe even 60?) of 24mpixel raw files. That pretty impressive =)
Most sport photographers are, by contract, not allowed to take moving images, especially at important events. Even if they could, the file sizes would add up very quickly so the video side of the 1DX range does not help sport photographers. I shoot sport and video, but both are separate and not at the same event. While I have used the 4K mode for video, I do not use it much as there is little point for what I am trying to do and it just makes the whole process (downloading, editing, rendering, storage etc.) take longer.