I know this is a very different game, but there's a game called cloud chamber, and while I haven't played the game myself, its a very interesting idea. Its more like a movie, but instead of the whole movie, its split up into different sections, and you play through it and you talk to others about the story. Maybe you could do a similar thing, only with more game play involved. So if you go through door A, the campaign will roll a little differently if you go through door b. Also, you could do it where the stories overlap, so your playing as one character in this part and then you go through door C and your a completely different character going through a different scenario, which if you made the story flow right I feel could be very interesting and thought provoking.