I think he means reconstructing a conversation by looking at quoted text (all the "On XYZ day, Joe Shmoe said:" stuff). If one person had been getting all the reply-alls of a conversation, he could create a discussion on your site, and forward a few of the emails. Your site would then reconstruct the quoted conversations.

It's quite a fuzzily-defined feature, because people don't always quote entire messages, they can change messages, and the characters used to mark off quoted text vary between email clients. However, it would be a cool feature to implement, maybe as an optional thing.