Do you think this kind of deep-threading, or tree-nesting, encourages a forked conversation, with everyone in the discussion trying to respond to individual comments in an ever-growing tree, rather than responding to the current conversation as a whole? I find mailing list threads that are trees very hard to follow. It's probably a conscious decision.
I've found trees encourage forked conversations in a good way. While I don't find them hard to follow, I do find revisiting them to be a bit difficult. While it can seem difficult to follow the overarching topic given a set of trees, it's near impossible to have any in-depth discussions about more than one thing in flat threads.
I have given these models lots of thought and have come to the conclusion that the success/failure of hierarchical conversations is determined solely by the presentation. Common mailing lists and email UIs leave the most to be desired, while HN, reddit, sbnation community sites, etc show a path forward. But nobody has implemented the view properly enough to let you see the forest and the trees at the same time (yet).
Here's a concrete example where I think it goes wrong. You say something, and two people respond. There's one thing to say in response to both people - maybe they both misunderstood part of your point. Which comment do you respond to? On places like HN people seem to feel the need to respond to both branches, which causes exponential growth if it continues, compared to if you could respond to the two comments as one. Maybe we need a comment DAG instead? Responding to an arbitrary number of comments? Maybe comments that aren't even siblings?
Internet messages (Usenet, email) already work that way. If you want to reply to multiple messages, this is easily possible.
Most users are not familiar with it because the widely implemented threading algorithm prunes the graph into a tree for display purposes. https://ddg.gg/?q=jwz+email+threading
HN comments are a DAG. DAGs are branchy, which is the problem. It seems like you want to merge or rebase the two comments and then reply with a new node pointing to the last of them.
