I can see the likes of Daniels, Mysterio, Anderson and maybe even RVD from Nitro taking part of the match while guys like Rhodes, Sandow, Jericho and Ziggler taking part in the Raw one. So I would feature them in the poster. Maybe not vertically but in an horizontal fashion but really only creative know who would be in the MITB and featuring them in the poster before they are revealed would be a major spoiler.
Maybe former MITB winners like Edge, Jericho, Punk. Swagger and such could be good. A high profile feud like Ambrose vs Rock, which I'm sure will be a big part of the event granted how it ends on SummerSlam or whatever. It's up to creative.