Seem like a pretty weak system. Even if you only trust alternatives from people you follow, how are the those people supposed to know what was at the original URL? Providing these alternatives seems like a highly specialized task that is likely to be done by relays or other third parties which makes it even worse. Only trusting the original author to provide alternatives is a little better. But how is your non-technical grandmother ever going to understand who to trust in this scenario?

Content-addressed media is the solution we really need but I don’t see an easy way to get it adopted.