Having a team of moderators *per* topic would work nicely, I think. Problem is, if you give ownership to the first person interested, how do you avoid topic-squatting? How do you hand over a topic, after original owners go AWOL? Reddit handles those *somewhat*, but I think it's stackexchange that got a lot of those things *right*. Problem is, they have a scoring mechanism that allows them to select "trustworthy" individuals. Maybe we could calculate 7d activity score for a new topic, and then propose top 3-5 posters to become admins?
Never designed a social site before, so my ideas are probably horrible :D