It would be interesting, but the duels would be difficult to implement, I tried to play a game of chess in an RP a few years ago and that took a while, but you'd have to be specific on the cards your decks contained, can't go pulling a random really rare/powerful card out of the bag somewhere, maybe everyone could PM their deck to you before the RP started? So it's only the owner of the RP that knows what everyone has, or something along those lines.