I think we're on the same page to some extent. What I meant by 'ranking by comments' is that we want the ranking to depend on the quality of the discussion. That's the one thing that can't be faked.

That's how the ranking of HN stories works now. It's a combination of upvotes and human curation by users (e.g. flagging) and moderators.

So there's going to be some combination of technical and non-technical factors. How exactly will that work? We don't know yet. Let's see what happens and figure it out together. That's part of the experiment: we'll figure it out in the open and adapt to feedback. But let's wait until we have some data to look at.

FWIW, my experience with HN is that genuine community interest is relatively easy to recognize.