I think this is counter to the way discussions naturally develop, where many topics and sub-topics appear “organically”, without foresight, and where it’s not always possible to predict what will be controversial and spur debate or not.
Personally, I think of an official SIP discussion, for example, as a process meant to create some form of an actionable summary of arguments for and against each SIP. The process should produce a clear document that can be referred to in order to be debated by the SIP committee productively.
This document can’t just be a huge, unstructured dump of messages in chronological order that mix threads, topics, sub-discussions, and trivialities. You often can see, in SIPs meeting, the SIP committee members puzzling over the Discourse topics trying to synthesize the main points with great difficulty, failing to be exhaustive.
Ideally, the result of a SIP community discussion should be a structured summary of points in favor and against, with voting enabled to rank them, and where one can “dive” into and expand each point and sub-points at will. I think this requires at least a thread-like structure. In my view, it would be closer to a wiki than to a chat history.