I will just add that my idea has nothing to do with the game campaign, modding, or mechanics. It's purely imaginary as given by the strategy map on vanilla M2TW, and the battle system. The real action takes place outside the game, on bulliten boards where you see all the information (reported by your spies, we assume in every region). The game is used only when a battle takes place (so we can just use the multiplayer feature as it is). But it's heavily dependant on your campaign strategy.