Not all designs generate the same amounts of heat, as long as the box can dissipate the amount of heat generated inside, it will not overheat. The Canon design generates a lot of heat internally, Sony has learned to reduce heat generation, a larger camera with more surface area can dissipate more, so I can conceive a much longer time to overheat as being possible at least. Remember, the Canon design is 2 years or more old, newer models will be improved.
I see 3 main areas of heat generation in the R5:
1. Given the 8K spec and dual cards, it would be assumed that it would have dual CFe slots. We know that they are hot spots from the R5 measurements. A larger body would be needed to dissipate the heat (however it is done) similar to the 1DXiii.
2. The sensor is the 2nd and the 1DXiii doesn't have IBIS. If the Sony (or R1) has IBIS then there needs to be a better way to move the heat. Fan/convection appears to be the only option here as IBIS doesn't allow significant heat conduction to the chassis
3. Processor/DRAM. Roger's teardown shows heat spreaders for the processor/DRAM but they would need to be bigger and better connected to the chassis. Besides clever firmware, a smaller node size eg 7nm is the best way to reduce heat generation and increase performance (and yield per wafer). It is amazing to think that semiconductor manufacturing average lead time is 3 months. Big problem if you have design flaws!
One option for the sensor size is for the R1 to have higher shutter speeds with interpolated resolution from whatever is native down to 20mp. Best of both worlds (high res for non-sports and 8K video and speed/low res for sports). Based on previous designs, a dual Digix X may be used to handle this (and maybe spread the heat generation by running each at a lower clock rate?).
"Pro" to me implies excellent weather sealing. Grip can be integrated or not but if not then heat management will have the same issues as the R5. The 1DXiii avoids 2 issues as it doesn't have IBIS or a larger sensor (and associated processing in certain video modes).
Excellent weather sealing from Sony bodies hasn't been their strong suit.
Peltier devices are inefficient, not small and are power hungry so it is hard to imagine them being used from the internal batteries. Heat pipe/sinks could be used to conduct heat into a separate chamber that is weather sealed from the internal electronics but vented. How to use fans within it and maintain overall weather sealing without low temperature burns from the chassis would be a challenge
It will be interesting to see what they come up with as well as the R1 to address these issues