Resurrecting proof-of-work for pull requests just trades spam for compute and turns open source into a contest to see who can rent the most cloud CPU.

A more useful approach is verifiable signals: require GPG-signed commits or mandate a CI job that produces a reproducible build and signs the artifact via GitHub Actions or a pre-receive hook before the PR can be merged. Making verification mandatory will cut bot noise, but it adds operational cost in key management and onboarding, and pure hashcash-style proofs only push attackers to cheap cloud farms while making honest contributors miserable.

Proof of intelligence might be better.

Hashcash: https://en.wikipedia.org/wiki/Hashcash

CAPTCHA: https://en.wikipedia.org/wiki/CAPTCHA