Actually, my business clients are mostly musical instrument manufacturers requiring maximum detail in very high quality images and often using those images in rather large print applications for trade shows and artist posters. Photos of their products could appear in brochures, on the walls of dealer showrooms, or on the side of a truck for that matter. The idea of being able to offer higher resolution images with exceptional detail is appealing. I can see an advantage to being able to crop these large images to call out extreme feature detail without having to add excessively to my clients' costs and size of their image archive. While the cost of the higher resolution images would be greater, the flexibility of capturing images from within larger images would offer offsetting economies. I may be shooting highly reflective metal instruments one day and portraits of their performing artists the next. Ninety-nine percent of this kind of work, of course, is created in the studio with the benefit of strobe lighting. High ISO capabilities are almost never the issue. I shoot almost always at 100 ISO thus the low light and noise issues some colleagues may experience are not normally issues of mine. For these reasons I feel that the 5Ds may give my clients an added advantage. The question of lens requirements to achieve the IQ levels I want is a serious consideration if I am to invest in the 5DS. At the same time, this hi-res capability may be achievable without needing to make a much larger investment in medium format solutions.

I have read here on the forum and in other places that the new 5DS or 5DS R requires L lenses to resolve images at 50 mp. I'm considering buying the camera and I own 2 "L" lenses. The question is...will they be adequate? I currently own a 24-105L and a 28-300L. Since most of my work is in the studio shooting product, I'm expecting that the 24-105 L will continue to work well with the new 5DS. I have a 5D Mk2 and a 7D Mk2 for other work. So will the 2 L lenses I have do the job? If I have to buy another lens, what should it be?

The II version is great, I couldn't agree more. It's very bulky, though. As you probably know, I also had, and still love, the Oly OMD E-M1, which was stolen. Its a helluva lot smaller and lighter, with good image quality and it spoiled me to a certain degree; but the 1DX with the 100-400 L II images are literally like shooting fine-grain film in 3D. Beautiful, and awesome for sports/action.
I know it's off-topic for the OP, but the II-designation lenses might just have been developed for the new 50 MP sensor+Digic 6. ;)