Obviously, there could be a high-res model: 80MP or something.
I'm hoping for a sensor with built-in ND, 16-18 stop dynamic range, and no rolling shutter. They have a patent for a dual-well sensor that could do all this.
Physical strength of course.
But what else?
hmm..
24MP
30 fps electronic shutter
Bird, Animal, Alien,Human eyeAF
1 series ergonomics
1 series build quality
LP-E19 battery, thus better battery life
4K240p
1DX Mark III's joystick
dual CFE
I doubt global shutter,etc. current sensor technology is more than fine.
the big draw of course, is that it will smell, feel, handle, and taste like a 1 series camera body to get the pros to convert over. I mean that's the main thing, other than that it has to match or exceed the 1DX Mark III's specifications in such a way to draw over the pros. your ideas on the sensor? not really necessary because most of the pros shoot jpeg that use the 1 series. I can't see that as a big migration draw from the 1DX Mark III. Sorry.
I think what will determine if the 1 series RF camera body migrates the pros well will be the lenses. I suspect dual linear AF super telephotos with extremely fast focusing - even faster then their EF counterparts. Probably not much size or weight savings, but simply faster. They may do some tricks such as matched DLO profiles for the super's so that each super telephoto has it's own generated DLO profile instead of a stock one. They may even pull out the DO stops with matching DLO .. that may make things alot better there as well. so you have the size savings of DO with the computational correction of DLO. Delicious.
what would be compelling is a 5G connection module that allowed for a continuous image.Canon connection and automatic distribution of images,etc. If they could pull that off .. well, that would be game over Nikon and Sony. Just call it a day, and make consumer cameras.
Other than that the main feature needs to be how this camera is for the working professional. EVF, performance, etc has to be top notch and better than anything else out there.