But I am confident these physics issues can be worked out to a sufficient level of trust.
Only need to confirm that the private key was not communicated from the computer to any one.
I find this kinda weak against your general absolutism. "So Simple Yet So Complex".
After all, what stops all 3 letter agencies, who can own blockchains and can do analysis and attacks etc, to stage the whole thing? Will i be allowed to check that computer?
I mean, i have near to zero understanding of cryptography, but your search for the perfect/ideal solution looks like making you ready to take a huge and dangerous bet.
I proposed ephemeral mixers based on Zerocash technology. They will be ferreted out if they are doing this, because it will be known that the key was compromised when the mixer expires and everyone has to cash out of the mixer back into the public coin. The bastards can't keep doing it over and over again. The participants will get wise as to the methods the attackers are using.
I am not absolutist. Rather I think correctly and realistically when I weigh marketing, tradeoffs, and delusion as follows:
That will kick ass on Monero, because if I pass through the mixer, I know my anonymity is provable and I know I didn't lose my coins. It is only people who still sitting inside the mixer who risk losing coins. Everything has a risk. I would much rather the microscopic risk of a compromised key (causing me to lose some coins) to the sure risk of meta-data correlation in Monero which can send me to jail! Surely I would be judicious about not mixing all my coins at the same time and not all in the same mixer.
Marketing and design are holistically joined at the hip. Those fools who said the marketing can come later are clueless.