I really just wanted to comment because almost no-one gets what you wrote about the importance of data-ordering. So the piece started strong, but then felt like it started tripping over itself.
On the permanence/immutability issue, I guess my opinion is that permanence is distinct from immutability and that while all blockchains require immutability, they can exist with varying degrees of data persistence. I tend to think bitcoin would be perfectly safe running on a 100 year chain with periodic hardforks to upgrade the genesis hash, for instance, and that it would be a bit strange to suggest that this wouldn't count as a blockchain, even if the trade-offs would make the network lose some properties of "digital gold". At a minimum, arguing otherwise would seem to imply that UBTC isn't a blockchain, which is obviously wrong.
On the permanence/immutability issue, I guess my opinion is that permanence is distinct from immutability and that while all blockchains require immutability, they can exist with varying degrees of data persistence. I tend to think bitcoin would be perfectly safe running on a 100 year chain with periodic hardforks to upgrade the genesis hash, for instance, and that it would be a bit strange to suggest that this wouldn't count as a blockchain, even if the trade-offs would make the network lose some properties of "digital gold". At a minimum, arguing otherwise would seem to imply that UBTC isn't a blockchain, which is obviously wrong.