I think you're onto something! A retrospective history of science styled as an HN clone would be amazing, will any of you dare?
Sure, not many, if any, clients handle an arbitrary list of message id's there, but it's clear[3] that's what it's for.
[1]: https://www.rfc-editor.org/rfc/rfc822#section-4.6.2
I'll search for examples of UI used for many in-reply-to, it seems interesting.
I have much more imagination than skills.
same!