After the R5, R5 C, and R3, Canon did not leave much room for an R1.
It will be basically for the people who are not satisfied with those 3.
The R3 is more than sufficient to fulfil the needs of most professionals. But manufacturers are always striving to provide more. So what are the few remaining areas where improvements would be beneficial, and where does that leave the R1?
More MP? - possibly, but that will only be useful if there are also options to shoot uncompressed RAW at lower resolutions, as 24-30MP is enough for 90% of images.
Global shutter? - possibly, but ultra fast readouts would reduce rolling shutter to the level where it became virtually undetectable, so global shutter may not be necessary.
8K? - probably, and that would need more MP than the R3 has.
Greater durability? - possibly, suggesting the possibility of dispensing with mechanical shutter.
Faster burst speeds? - possibly, but the R3 is already pretty damn fast.
Better eye-controlled AF - definitely, as the R3 is less than perfect in this regard.
Better AF tracking - almost certainly there are advances to be made in subject recognition, AF acquisition and tracking.
Better EVF - definitely, higher resolution, more natural rendition, and reduced lag time are all needed.
Faster file transmission - definitely and of increasing importance to pros competing to get images to the media rapidly.
Pre-capture? - definitely, sports, wildlife and reportage photographers all want pre-capture, but it requires a powerful processor, a huge buffer, and very fast readouts.
AI? - possibly, AI could be used to increase resolution, DR and sharpness, and to reduce noise and motion blur, all of which could be baked into the original image.
The next question, is how much extra, over and above the R3 price, would buyers be prepared to pay?