Hmmm, lots of possible direction here.
Consider the known "R" as the intro model, and take on board all the features and functions and flanges that came with that. Also consider 8-fps, but only in one-shot mode. IF you want to have AI-Focus, then it drops to a lazy 5-fps. So look at the "data-bus" on that stream, and at the very end is a single SD-Card. OK, so it is a quicker SD, but it is still "just" an SD-Card. Consider all the clever techie bits that happen before and after the "shot" and include those considerations when thinking about some bigger brother R+ thing.
Then go look at the normal "life-cycle" for assorted Canon camera models. How frequently did they do Mark-i, Mark-II, Mark-iii, Mark-iv. (for both the 5DS-R and the 7D)
Now join up all those dots.......
Loose the SD-Card and give me a C-FAST, or even TWO nice C-FAST cards
Give me all the low-light and dynamic range of the "R" sensor, but add all the missing pixels to get me up to 50+
THEN, get all fully tricked out on the software front. DO the CROP in software. Give me a builtin x1.6 like I get on the 7D, which would CROP the pixels from 50+ down to 30+ and so I also loose some of the 5000+ focus points. Having "only" 2000 focus points and 30+ megapixels means there is less data going into the "Bus" and so you can do that faster.
So 50+ megapixel at say 9/fps (Nice!)
And 30+ megapixel at say 12/fps (also Nice!)
Dual C-FAST cards and hence all the focus towards cine-camera and high-frame-rate slow-motion movies.
The 1DX Mark-ii is a beast, I bought one shortly after the announcement. Major league, in your face, industrial strength PRO camera for all the photo-journalist folks doing sports and action pictures.
The 5DS-R is also a beast, but mainly for fashion, macro, product photos.
The 7D Mark-ii is then the crop sensor, wildlife photography tool (desperately in need of an update)
By all means start working on a "R" variant of the 1DX replacement, but makes much more sense to combine the 5DS-R/7D replacement into a "R+" body and announce same in January, immediately after my nice employer announce what the nice bonus payment will be.