Or here's another one: Sort of a "Dungeon Mastering" the campaign. One players is the protagonist and the other, the DM, is an antagonist with limited options and reinforcements to throw at the player. That could be a loads of fun. It would be a dynamic campaign with unpredictibility of the human factor, utterly filled with a lot of "oh sh*t" moments and evil grins followed by maniacal laughter.
It would be some experience to have and a lot replayability.