It's obviously feasible to make a high MP camera in a 1-series body, but then it becomes something that it probably wasn't intended to be. The "problem" with high MP is that sports photographers would generally prefer to have unlimited buffer and more reasonable file sizes, rather than a crazy-high resolution that they don't need for their media format (on line or magazine). If you're wanting high MP to make 8' wide landscape photos, I am guessing that you are probably content with the R5-type of body that has lower fps and a smaller battery.

If it's possible to have some kind of selectable resolution (other than digital cropping), then maybe it could be the best of both worlds. For example, have an 80 MP sensor but use a super-compressed RAW option to make it perform like a 40 MP sensor when you want it to. Is that even feasible? If so, then you would suddenly have half the file size and twice the buffer when you didn't need the full resolution.