> I think the current model lwn has is best, overall.
I tend to agree; the advantage of a hierarchy of replies is a great deal of structure. That said, the best system would be one where chronology is even more clear. Example: I may read the original post, then a reply to it, then a reply to that, then I might reply to the original. Because my reply is to the root I become a branch from that even though, chronologically, I also follow the second reply. The contents of the second reply may influence what I write, but the only way to tell that my reply actually came afterwards is to do timestamp cross referencing.
In a more relevant example: suppose I reply to myself with a correction. Which replies to my original read the correction before replying to the original? It would be nice if there were a way to tell (visually) without losing the hierarchy.