I watched the whole video twice. I think you should watch it again. No way Apple should take on trying to repair an iMac that was abused so badly. They could plug in a new logic board and have it burn out for whatever reason the first one did. Who is going to pay for that part? There is now way of knowing the condition of this machine. Hard to muster sympathy for somebody who purchases a $5000 iMac Pro so he can make a tear down video, breaks the computer horribly and the expects Apple to assume liability and risk in trying to fix it. Best Apple should do for this guy is let him order the parts that he thinks are broken and let him try to fix it. But that’s not what he asked for. He asks Apple and an Apple certified repair shop (who clearly didn’t want to touch it and have him some BS false story about certification) to fix it.
People break their computers while tinkering with them on a regular basis. We've seen a lot on this forum alone. A famous example would be almost a decade ago, when Anand of Anandtech broke a Mac Pro that he was reviewing, by taking it apart and installing new CPUs to check for compatibility. See
https://www.anandtech.com/show/2800/upgrading-and-analyzing-apple-s-nehalem-mac-pro/11. It isn't uncommon at all for reviewers to occasionally break things during reviews, even for experienced technologists like Anand. To those who think in terms of car analogies - car reviewers regular damage and even trash their review cars during reviews.
The review was even titled:
"Frying a Mac Pro - Upgrading and Analyzing Apple's Nehalem Mac Pro". His experience then went on to guide a ton of others, including those on this forum who upgraded their own classic Mac Pros. In his review piece, he noted:
"Thankfully, the folks at the Crabtree Valley Mall Apple Store in Raleigh, NC are AnandTech readers and quickly understood what had happened. They ordered the replacement part and I waited. If you’re curious, it’ll cost a bit under $400 to replace the processor board in an 8-core Mac Pro provided you allow Apple to keep your dead board." You can easily argue that perhaps the broken board had ramifications down the chain and that there may be additional parts that need replacing - but that was obviously conducted on a need-to-verify basis without prior assumptions (and damages like this are usually self-limiting because of numerous fuses on most modern logic boards). If no one wanted to take a risk to repair something, then nothing will get repaired. There wouldn't be any of those repair stores and channels like Louis Rossmann's.
What you subjectively call
"abused so badly" doesn't mean anything in the context of a repair. There can be catastrophic damage resulting from any gentle usage, like a power surge beyond the owner's control. There can be simple damage from a sloppy disassembler, like detaching the fan connector from the board. Anand's example can certainly qualify as "abuse" by some - he violated the warranty, upgraded the CPU, bent a bunch of pins in the socket, didn't notice any of it, reassembled the computer and powered it on. How is this wildly different from what Linus did? We don't even know what the extent of the damage is inside Linus's iMac Pro, all we do know is that everything can be repaired and that he's willing to spend whatever it takes to repair it. There are only a finite number of modules inside the computer - logic board, power supply, LCD assembly, speakers, cooling system. Replace enough of them, and you've effectively repaired the computer. That's if you don't have Louis Rossmann's component-level diagnosis and rework skills, which means there are obviously lots of others who can module-level to component-level repair his iMac Pro. The issue here isn't this BS about whether or not there is risk associated with the repair, or that there would be liabilities - there will always be risks and by Anand's example and countless many others, precedent HAS BEEN SET. HP and Lenovo for example, will sell you whatever part(s) you need and if you acknowledge that you are comfortable with installing it, you take the responsibilities and they send you the part(s) to fix your computer.