I found myself thinking a few days ago that half of threading on Twitter could be implemented with simple microblogging and a protocol for back-reference URLs (all of which can be done in something as simple as hugo or Jekyll) coupled with a standard for the user-agent to "unroll" the thread. This requires neither a centralized or federated service; it's built on basic web tech.

The only piece of the puzzle missing is that it only works one way; to see the whole 'conversation,' you'd need to find the tail of it (most recent comments). This sort of data-mashing is one of the things a centralized server can do simply and well (though it's certainly implementable on a federated service). But without a federated service, a rule for semantically identifying "topics" and web-crawler that knows how to sort by newest-to-oldest on a given topic identifier gives you the whole story.