Scarlet's intention is to change the notion of a 'DSLR' by shifting the paradigm by which you capture stills by merging stills capture into video. By that we don't mean tacking 1080P on to a stills camera. Instead every frame of a clip is worth of a still and every 'still' can be a burst of frames so you always get the moment at 30 or 60fps rather than 10 fps.
We have alot DSLR shooters at RED and yes, we see Scarlet replacing our DSLRs.
For $40,000 for two full-frame systems, for more than 3 times the weight, without fast autofocus, and without a flash system? That's just nuts. Taking professional-quality video prevents the taking of professional quality stills. I might change focal length by a factor of 5, aperture by 5 f-stops, the direction I'm pointing by 120 degrees, and go from flash to non-flash, all in a second. The resulting stills are just fine, the resulting video is a throwaway piece of garbage.
30fps and even 60fps is often too slow for the "spray and pray" approach anyway. These pairs of images were taken by different cameras, at obviously different times, each taken in single-shot, and they are timed within about 1-2ms of each other. You'd need 500fps to 1000fps to do that with spray and pray, yet I can do it fairly reliably (over 50%) with single-shot, even though these two cameras have different amounts of lag.
http://photos.imageevent.com/sipphoto/samplepictures/20D versus S3 crops.jpg
http://photos.imageevent.com/sipphoto/samplepictures/20D versus S3 crops 2.jpg