MP campaign would be great, but as for the majority of posters here, I don't see it as very practical.

Possible workarounds;

The 'order' turn sounds about right above, these could be made offline, and submitted into the game (though how this works in terms of whose computer the game actually runs on is not for my non-technical brain to work out).

As for the real-time battles, perhaps each faction could only fight one per turn on the battle map, (choosing which one), and have the AI fight with the rest of your armies. This way each human player fights one battle per turn, against either human or AI adversaries, thus not slowing things down too much. the human-AI battles could also be fought essentially offline.