I think the biggest value proposition of this is the ability to do sub-reddit like filtering on specific tags. As Hacker News grows I think dealing with the number of new submissions would become a bottleneck. During high-traffic times, new submissions sometimes drop of the first 'new' page in around 10 minutes. Of course there is more traffic during these times to upvote good content, but I'm not sure that is better than letting a smaller number of people have a longer period of time to filter a smaller collection of content.