Stephen is spot on, the 1 series has historically been focused upon a fairly narrow market segment with a brief aberration into the "studio" S suffix variant. Fortunately, the 1 series has stayed focused upon its target market needs.
For any level of sensor technology, a smaller pixel count with larger photosites will provide better low light performance than the same technology with a higher pixel count and resulting smaller individual photosites. For those of us doing a lot of limited light shooting, how the sensor performs in terms of noise and DR in limited light is critical and I wouldn't hesitate to choose a 20 MP sensor with significantly better low light performance over the prior generation instead of a new 30 or 40 MP sensor that only delivers equivalent low light performance to the prior generation. As to data processing/workflow/storage, any system that handles a 40 MP sensor image well will handle a 24 MP sensor even faster. I use twin CPU HP workstations for photo/video work and you can NEVER have too much processing and storage but you can definitely have awkwardly large files.
As to file size, it IS what the 1 series market wants and Canon has a long history of success in this market. The other even more critical requirement for the 1 series market is near perfect reliability and that is what I will be watching most closely before even considering making a transition from my 1DX III bodies to the R1 and quite frankly I have not been impressed with that aspect of the R line so far so the R1 needs to get it right. Miscellaneous unexplained lockups, overheating, random glitches, and the like are not acceptable where the 1 series plays. The 1 series has to offer rock solid reliability under conditions that the photographer hates to work in and I have experienced that plenty with my 1 series bodies in over two decades of 1 series usage.
Pixel count is one measure of performance but one that the consumer market is fixated on, see phones for example with ridiculous pixel counts using a tiny sensor and "just good enough" optics. There has long been a parallel in the transportation/logistics industries where many consumer diesel pickups have higher horsepower ratings than semis BUT a truck powertrain is perfectly focused upon its intended market. You can't fit 16 liters of engine in a pickup truck engine compartment, the front suspension won't support the weight, and the customer wouldn't like the price/performance/handling. And a commercial firm expects to get into the million mile range before a major overhaul on a semi-tractor powertrain which spends long days 7 days a week hauling heavy loads and a small displacement light diesel won't deliver that under sustained heavy usage. Both transportation choices are built for their specific markets and if someone buys a product intended for a very different market, they won't be very happy with the result.
I own two extremes in the Canon line, with a pair of 1DX III bodies and a pair of 1DX II bodies but also a little "baby" M6 Mark II purely as a light small convenient camera for use where I don't need a "real" camera but want a camera that handles like a camera instead of part of a phone. I also own a pair of 5DS R bodies but if high MP count becomes a focus, I would be looking at medium format systems.
Rodger
EOS 1DX M3, 1DX M2, 1DX, 5DS R, M6 Mark II, 1D M2, EOS 650 (film), many lenses, XF400 video
