How about a Fantasy Role Play forum?

I've seen several sites dedicated to this, where two (or three) users post a role play scenario and alternate adding to the story. They can get pretty hot. Aside from being a good read, we get the addd benefit of being able to act these roleplays out BCD. Only members with PA, or verified provider status should have access.

Only issue I see is preventing people from hijacking a thread.

See http://bluemoonroleplaying.com/ as an example.

http://www.eccie.net/showthread.php?t=805084

Great example of how it could get hijacked by random users and turned into something really lame. If only there was a way to limit the thread posts to just the OP and one other person, it could work really well. At the end it could be opened up to comments.
Not sure if the site supports that...