> Is there a way to aggregate and rank content without an authoritative server?

Something like RSS: Pick up all posts tagged such and such from these users.

I've thought a bit about this and if we really wanted to we could get really far with just a few hundred lines of code as well as some html templates.

Problem is, most people like facebook and instagram :-/

RSS doesn't really have a method for 3rd parties to rank content, does it?

The thing about HN is voting and comments, both of which require manual moderation to be effective.

Couldn't the moderation be distributed as well? Pick the moderators you want and the posts are filtered with their moderation actions.

Agree, I could share (a subset of) my sources as could you.

We could even automate it so if my post reader notices several of my sources following another source it will ask me if I want to look at or follow that source, etc.

Then 'most people' aren't your target audience. That doesn't mean there isn't a well sized target audience.

Usenet / NNTP

That's federated, which is a different kind of decentralized than the one implied in the article. Federated systems are less centralized, but still require regular clients to trust the system they are federated with.