It's probably not trivial to implement and there's already a bunch of problems that need solving (e.g., trusting keys etc.) but... I think that if we had some sort of lightweight code provenance (on top of my head commits are signed from known/trusted keys, releases are signed by known keys, installing signed packages requires verification), we could probably make it somewhat harder to introduce malicious changes.
Edit: It looks like there's already something similar using sigstore in npm https://docs.npmjs.com/generating-provenance-statements#abou.... My understanding is that its use is not widespread though and it's mostly used to verify the publisher.