An R1 which is the form factor of the 1DX would get more shots per charge, to start. Global shutter would be a differentiator. Quad pixel AF another. If the R3 is getting effectively the same IBIS as the R5, Canon's v.2 IBIS. R3's eye control v.2. Increased processing power for crunching through high-res video, as well as photo processing to make the cache effectively limitless. There's a lot an R1 could have.I agree with all your points. On the R1, I also believe that Canon is in no rush. In fact, other than dual CFExpress card slots, I'm not even sure what Canon might add to an R1 to distinguish it from the R3 and justify a higher price. It seems that with the 1DxIII and the R3 (if it delivers as promised) Canon has the sports and photojournalism market very well covered.
For me, that raises the question of what niche would an R1 target. An R1 might be compared to a Leica. Built to professional standards, but actually marketed to enthusiasts who are willing to spend top dollar to have the best camera Canon makes. To further argue this, I look at the traditional market for the 1series bodies and there is no doubt that the professional market is shrinking fast and those that remain are being squeezed financially, making a lower cost R3 more appealing.
That means we can throw out all the old assumptions about the 1 series and possibly see specifications that will appeal to high income buyers more than professionals (such as a 45+ mp sensor).
It's also possible that with the R3 and 1Dx III available, Canon would like to get back on the four-year schedule for the 1 series, pushing a development announcement out to 2023 and actual release early in 2024. This would also give them time to perfect any new technologies that could separate the R1 from the R3. That might mean that the R3 will be a one and done series.
Canon does seem to be on an aggressive development cycle for the R series, building out their lens selection by replacing EF lenses with RF counterparts and adding new RF lenses at a rapid pace. They already offer more R bodies than they ever had in full frame DSLRs, with more rumored to be on the way. I'm guessing that the other rumored R bodies (low cost or high megapixel) offer greater return on investment than an R1.