Ask HN: Would it make sense to decentralise social media with PGP?

I tried to find an easy way to stream news in real time. Twitter API is a natural choice, but I couldn't bother to sign up after it asked for an essay on why I would like to use the service. This led to another thought.

Several social media platforms such as Twitter and Reddit are mainly based on public content. There is no real reason why they should be centralised like they are. Signed content could be broadcasted instead and the receiving nodes could identify the sender by their public key. (Public keys could be registered on a keyserver that requires demonstrating ownership of the email address in the key.) Content could later be requested from these nodes and it could be compiled to a news feed.

Does this kind of thing exist already? Is there a reason why it wouldn't make sense?