While not a perfect solution, perhaps you could tag various conversations by subject and keeping track of which topics a user tends to discuss. If a user mostly talks about a few subjects, have their comments in conversations with those tags be prioritized by the ranking algorithm and deprioritized outside of it. Obviously just because you spend a lot of time talking about something doesn't mean you actually know much about it, but it's a start. Perhaps you could improve further by keeping track of users' karma within a topic (presumably those speaking from ignorance will be less upvoted), but this runs the risk of promoting views that are popular instead of informed.