The inability to field a preset army in multiplayer with partial units is the biggest thing preventing players from seting up their own multiplayer campaign. Half of this is already in the game with the logfile that's created after a battle. The logfile represents an army stack on the strategy map, but inputting that logile, which contains the results from previous battles, into the next battle is missing. You would also have to be able to move units between logfiles and possibly combine partial units, but a tool could be made to do that by someone in the community.