We've worked on things like this in the past without success. Even just saving the html of the web pages that get submitted to HN is a nontrivial problem, and extracting text from them for similarity searches even more so. If people wanted to work on this as an open-source thing, we'd be open to supporting it somehow, but it'll be quite a while before we get back to working on the problem at this level ourselves. I think relying on the community to co-curate related-links lists (and duplicates) is likely a better and easier strategy.