>On the other hand, long threads pick up too much baggage nobody is going to read

I think the key here is, if you don't want to read what other people have to say, why are you here? Suppose it's a discussion on a technical topic. Maybe people have gone off on a tangent that should have been split off into a new thread/topic, or maybe the discussion being had is necessary context to get an idea of where the real answer lies. Reddit-style threads make it easy to have back-and-forth discussions, but at the cost of punishing long discussions with less visibility, or even with worse UX (given the increasingly narrower horizontal screen space as the conversation goes on).

Honestly, want to know who actually has this figured out? 4chan. See a comment, besides it inherently linking to the comment/s it's replying to, you can see at the top of its box a list of child comments that have replied to that comment, and if you hover over the links you can get a quick view of the comment to decide if you're interested (before committing to changing the scroll position), but comments are still listed chronologically, so if you just want to see the newest comments on a thread, it's still possible to do that. Famously, few years ago a stickied thread on /trash/ went on for months and tens of thousands of replies. Something like that would never work on Reddit or HN. Well, I mean, people can still make top-level comments, but after a while no one will see them.