[thisAintNoGame]

I'm not sure machine learning algorithms are the right approach. Crowd curation mechanisms (i.e. the upvote/downvote systems but one could imagine other systems) have the advantage of quickly adapting to the ever changing tastes of a community. I don't think machine learning approaches can be simultaneously good and flexible in such a diverse environment. The Netflix analogy isn't the best because Netflix deals with a pretty structured problem in comparison to the "recommend me things on the internet that I will like" problem.

I will also claim that subreddits are by no means a hack. They are THE key feature of Reddit that allows users to join together on the basis of common interests. There's no replacing subreddits because they are a killer feature in their own right.