If we imagine for a moment that it were 24 or 30fps continuous- could that output be used for video as an alternative to the designated video modes? What would make the results different?
The difference is similar to the difference between JPEG and RAW in stills. You get a lot more flexibility in post and can usually capture a little more dynamic range. There's a video comparing RAW video to H.264 here: https://www.youtube.com/watch?v=jkSYIzCgdIk
20 fps is almost there (playing at 24fps is a 12% speedup), but how long can you practically record at that speed?