Maybe an option, but I like that the top comment is usually above the average quality for that thread. Maybe something like a multi-arm bandit could work, where

Maybe an option, but I like that the top comment is usually above the average quality for that thread. Maybe something like a multi-arm bandit could work, where the nth top comment 'slot' on the page has an 80% chance of being the nth most upvoted comment, and a 20% chance of being a randomly selected comment?