It wouldn't prevent a project that has a goal of being purposely malicious, just from pushing out releases that aren't actually releases.

As far as who to trust, I could imagine the maintainers of different high-level projects helping each other out in this way.

Though, if you really must allow a single user to publish releases to the masses using existing shared social infrastructure. Then you could mitigate this type of attack by adding in a time delay, with the ability for users to flag. So instead of immediately going live, add in a release date, maybe even force them to mention the release date on an external system as well. The downside with that approach is that it would limit the ability to push out fixes as well.

But I think I am OK with saying if you're a solo developer, you need to bring someone else on board or host your builds yourself.