What if HN could have a "related post" option? If you remembered (or searched for) the older post, you could then link a given post to some other post.

Oh! And then you could have people rate the relationships, just like they can rate comments!

Oh! And you can put it into the API, making everything into a linked list of stories!

Yes, let's make the schema even more complicated 8-)

Edit: To be clear, I do like the idea.