I think "Collaborative fiction writing" is good, be cause this needn't be just for fun. The 'Wattapad' platform mentioned by OP has made some of its users best selling authors, so if WikiTale is done right it can become a lucrative platform for many.

Reg, locking the "tag"; I agree with Shweta that the tag needs to be dynamic according to the comments and locking it should be purgative of moderators only.