Earlier quoted context omitted.
You could probably just have a dumb bot post all prior links to the submitted URL with # of upvotes and comments for each one, then leave it to the readers to sort through which are interesting. I’m sure you’d get at least some folks digging through and reposing interesting/informative comments from previous discussions, helping stimulate the current discussion. Not perfect but good enough and relatively simple.
Totally agree! but then the question becomes how to fit that in the UI in a way that doesn't break HN's minimalism.
Just have the bot post it as a comment in the new post’s thread? Optionally sticky that comment, but probably not necessary, it will probably be voted near the top.