(I just added it to https://news.ycombinator.com/highlights)
Rather than autogenerating them, I think what we'll do is add software support for the community to collaborate on the 'related 'list for a post. And it needn't just link to related HN threads - it can be related URLs on the same story, for example.
When we'll actually get to this is another question of course...
To filter further, the list could just include posts with some points + comments ratio math. Also filter out similar posts within a short timeframe, if two posts happen within a week of each other, pick the one with the better ratio math.
No need to involve the community in moderation a second time, since they've already involved themselves with points/comments to begin with.
Jet Powered Volkswagen Beetle https://news.ycombinator.com/item?id=28349589 (August 29, 2021 — 2 points, 1 comments)
Ron Patrick's Street-Legal Jet Powered Volkswagen Beetle (2006) https://news.ycombinator.com/item?id=16513835 (March 4, 2018 — 156 points, 60 comments)
Street-Legal Jet Powered Volkswagen Beetle https://news.ycombinator.com/item?id=5384390 (March 15, 2013 — 6 points, 2 comments)
Street Legal Jet Powered Beetle (2006) https://news.ycombinator.com/item?id=831185 (September 18, 2009 — 76 points, 23 comments)