I would not be replacing the scanner. It remains my primary tool for image capture because it does such a great job. I only use my camera for artwork that can't safely contact the scanner bed. The camera I have used has done OK but I don't get the same resolution as the scanner. When using the camera, I use a copy stand with daylight lighting, which is limited in size as compared to the scanner. I haven't needed (so far) anything more elaborate.
The largest piece I've scanned was 48"x60", which came out beautiful but required scanning lots of sections and then stitching them together. It worked out fine but was a lot of work. I've wondered if a high resolution camera could get an acceptable image of a piece that big without all the effort. Hence my interest in the 5DS. I just don't have the $30K to $50K for a medium format camera, but could spring for a 5DS.