Many people including me are curious how 4k-images from the fs700 will look like. But the answer is to some extent already there: When shooting photos in photo-mode the results are cropped but in full resolution (1 pixel in the photo = 1 pixel of the bayer-sensor). So the photo-mode can be used to get an idea of how at least the quality of the 4k-raw-data will be. Of course the final quality will be higher because of the ability to fully utilize the 12bits/pixel and better debayering in software.
I did a test: I took a photo and a video with the same settings (cine2, detail -7), scaled the photo down to 50% to match the video resolution (vertical resolution drops exactly by 50% from 2160 to 1080) and put them side by side for direct comparison. Additionally I converted the result to Lab-color and extracted and normalized the a-channel for comparing the chroma-resolution:

http://dominik.ws/fs700/still_vs_video.jpg
(On the left is the photo, on the right a grab from the video)

It is very apparent that the picture quality improves dramatically. Also the the chroma-resolution increases, which leads to better chroma-keys.