Whatever happened to SHA-256 support in Git?

This part of the article is what stuck me, too. Git has been around for nearly 20 years now. There are vast amounts of existing git repos with sha1 identifiers in them.

I'd say the project is at best 50% done if there's no interoperability with sha1 repos. Even if you switched git to default to sha256 on new repos and convinced all the major hosting providers to rewrite the history on all their repos to sha256 today, it would be years of pain before that trickled down through all the repos in the wild.

Unless there's compatibility with sha1 repos and a nearly automatic way to rewrite existing repos to sha256 in a compatible way, then it's essentially unusable. That seems like just as big a problem if not bigger than making git capable of using a different hashing algorithm.