Awesome! This strikes me as a very good thing, especially with your suggested social norms. I have 3 additional suggestions, though:

1. Add a social norm where commenters make short summaries, or quote a couple sentences of new info, without the fluff. The title of the link serves much the same purpose, and gives readers enough info to decide whether or not to click through. This is standard practice on the more intellectual subreddit, since they already have the background context and knowledge that 90% of the article is spent explaining.

2. Add a social norm where the best comments get linked to. I enjoy Yvain's SSC posts, and the comments section often contains some gems, but digging through all of them to find the gems is tedious. I intend to quote or rephrase gems when I find them, and link to them in comments here.

3. Maybe we should have subreddits on LW. I'm not sure about this one. Tags serve some of the same purposes, so perhaps what would be ideal would be to subscribe and unsubscribe from tags you're interested in. However, just copying the Reddit code for subreddits would be simpler. It would divide up the community though, so probably not desirable while we're still small.