What I like about the concept of a Mobian IOT (or hell, any kind of province game) is the unique world offers chances to make the setting very different. I don't think any IOT has chaos energy applicabilities or mass furries yet! (Thorvald's IOT IV Mk II will be an exception if he gets around to it; I hope he does as I already made a background and even some pictures for it!)
I think I'd have some sort of income system since that keeps things interesting. NPCs have to be kept to a minimum though.
War will require special regulations; the Mobians generally aren't warmongers. That's assuming we use a preset setting rather than a wholly original one i.e. after a Cataclysm.
Use for income would probably manifest as army size, army quality, economic development and of course, good ole fashioned bribery. Techs are nice but can add a bit too much complexity.
The Industry system of IOT V could probably be useful in the economic development segment.
Think I'd make armies free to maintain, but the catch is any province without one(provinces can have individual armies in them due to how few in number they'll be relative to other IOTs) can be captured instantly. I'd cap armies too based on nation size + maybe some benefits.
Probably add special national powers each player can assign themselves to add some flavor, but keep it less complex than the Sliders of SoM.
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TK had the right idea with a victory condition, since it gives us all something to strive for and thus keeps the game lively and beyond "OMG BLOB ALL OTHER NATIONS. 83"
I imagine there'd be:
-Economic Victory: Control an economy 25-33% the size of the entire world's.
-Diplomatic Victory: Have a majority of the world's economy and militaries elect you leader; unless humans troll, chances are this won't be attainable due to me keeping NPCs low.
-Domination Victory: Control 2/3 of all economies and militaries directly or by proxy
-Chaos Victory: Build a Chaos Containment Chamber(expensive!) and collect all 7 Chaos Emeralds, allowing you to perpetually harvest their power for your ends
I think I'll make it hard to actually annex a state, so you have to be innovative and do something besides the forum game equivalent of a tank rush.