I think you're right in that it's so far not been necessary to use blockchain based identities. Though, I think blockchain based identities are objectively better. In implementation, it doesn't have to be a random person, it could be anyone or any organization that could endorse changes.
> I'm not sure how a wholly external PKI could be any help in "endorsing" edits. A user's ETH wallet has no relation to their reputation or trustworthiness on WMF sites.
Ethereum based identities are easy to remember and harder to censor. If Wikipedia wants to censor someone currently, they can just remove the system they have implemented. The solution offered provides an external system that provides a way to determine if someone did something even if Wikipedia tries to hide it later. (with the certainty that also backs billions of dollars in value on Ethereum)