Here are some I would like to see or start:
Word Games (wordgames.madlabs.com), mainly because some people like em and some people hate them, this way they can thrive with the folks who like them but those who don't can always not subscribe to this community.
Politics (politics.madlabs.com), it is a big enough a part of a2k that it deserves its own community (which would coincidentally allow a2k to be less political and more general).
News (news.madlabs.com), just for links to news as it breaks.
ConflictingViews (ConflictingViews.com), an old forum that merged into a2k, restored to be focused on debate.
Philosophy Forum (philosophyforum.com), this group will be restored to its original domain and revived as the main community for philosophy.
Water Cooler (watercooler.madlabs.com), for general chat. Not restricted to any particular subject etc.