Where I think HN will need to change significantly is in the way submissions are handled. Currently you need a score of about 4 - 7 in the first hour to make the front page, as the number of users increase, the score threshold increases with it. HN is at the higher end in terms of front page quality, but there's already a lot of good stuff that gets missed. Ultimately that will be compounded as things go on unless something is done to cope with it.