Although I would love to have this implemented, it is too manipulatable. Someone could have already come up or have already written a short story in advance before challenging someone to a duel and the other writer would only have the short window of time to think of one.
Good idea in theory, but too easy to cheat and just plain impractical for the mods. But I would love to see a duel that had to do with skills or creativity rather than chance.