I am surprised by the number of people talking about adding vents or a heat sink. Do you really think Canon hasn't physically engineered the camera as well as they could to handle heat dissipation? What would vents do for you without active airflow going through them? And adding a fan that's not just an external accessory, but an actually integrated component, just gives the people who complain about video on stills bodies a valid talking point.
If a hardware fix is coming, I would not be shocked if the cause of overheating is partially related to Canon not being able to manufacture or source the quality of components they had planned due to the pandemic. And the 'fix' simply being switching a part (simply used very lightly here, of course that is significant effort for product integration)
I attribute the reduction in CIPA battery numbers despite the increase in capacity to the IBIS. But I'm not even certain if CIPA testing requires IS to be engaged. If it isn't, it may well be that the R6 and R5 don't get all the new hardware with the greatly improved efficiency we saw in the 90D and 1DX III (where CIPA numbers went way up compared to the predecessors). It seems the 90D production isn't going too well at the moment. At least I have a friend who just bought one and said he had real trouble finding a store that had it in stock (very anecdotal, so don't make to much of it).
It all seems unlikely to me though. If they do something in software, it's probably offering more line skipped video options and giving you a way to accept toasting your hardware, like on the Sony.
I feel like all this speculation and acting as if the cameras had an actual problem isn't helping anyone really. We have now heard what the camera isn't capable of. But the reviews and testing on what it can do are very sparse so far. What is out there seems to indicate that especially the R5 is a remarkable leap in technology and should make buyers very happy. I am torn between it and the R6, an since stock seems to be an issue, have no problem with waiting a little longer to see how it all pans out.