I don't suspect my shooting style will be susceptible to overheating. I shoot in short clips. I also typically shoot in FHD and IPB the majority of the time. I didn't like the crop in 4K for regular shooting on the EOS R, and didn't like the large file sizes on the 5DMkIV. I will probably try to shoot in 4K now that the codec is fine and the crop is gone. Although, I can still see myself using 1080p.
8K is going to be a specialty thing for extra reach, and giving me the ability to 4X zoom/pan with no loss of resolution in 4K... and even 8X zoom with no loss of resolution in FHD. I'm actually super curious about the latter. I actually look forward to doing the whole "Enhance!" joke.
The 4K120P is what I'm super excited about because the High Frame Rate modes in previous Canon's were mostly unusable to me because of the soft and grainy looking 720p and lack of autofocus.
For both of these specialty features I have no intent on filming longer than a brief moment. The 120P will likely be less than a minute. And the 8K will probably top out at 5 minutes.
I'm happy with IPB for the majority of things so I may not ever see it overheat ever. lol. If I were going to make the decision to use All-I, oversampled 4K, or extensively use 8K... this is going to be for a planned shoot. I would be story-boarding, account for time of day for lighting, etc... so I would likely have to include the heat management in the planning and execution. I'd probably pack a cooler w/ ice packs.
I can see at the worst, wedding videographers maybe having the biggest legitimate gripe. If it were me, I would honestly shoot in the lower quality 4K24p with the occasional 60FPS for slo-motion, because then I'd have unlimited shooting time and I don't think my clients are going to be able to tell the difference. If they were distinguishing clients who wanted amazing footage, then it's going to cost them. I would need to rent the proper gear for the job in that case.
The outrage is funny to me, because even on both ends of the spectrum, nobody has had the final production model in hand and people are speaking as if their viewpoint is fact. You're just going to have to use it for yourself in your specific use case or at least wait until it gets real world reviews. I fully intend on testing if I have overheating problems for my work flow. And even if it does, I already have measures in mind. My favorite is finding a convenience store and throwing the R5 in a refrigerator for a couple minutes.