I'd have a randomly genned grand strategy HOI game, that plays out like total war: world wars, and is coop multiplayer like those coop starship/submarine/airship games that keep cropping up, with various rolls. A bit of OTTD would be thrown in, and the economy would be based off the first sim city, with different tiles producing different resources (ex, city makes money,). Random generation would create unique units, but everyone would be able to build the same thing. Units would be incredibly easy to produce, and losses would be very replaceable, creating a war of attrition feel. The amount of units you could build would be capped by your resources. The coop multiplayer would be where various players run different parts of the nation. You'd have different HQs each lead by a player. You cannot choose who goes where. SHQ runs the nation, selecting what goes where. Research decides what weapons to research and decides what a squad/tank/arty unit should have in it. And so on and so forth. There would be the diplomat/spy, the Generals, the Researcher, the SHQ, Airforce commanders, and Admirals. Generally the game would last a good amount of time, being drop in drop out multiplayer. It would be like vicky 2 and likely last 100 years. 200 tops. Thus it would add diplomacy, and make warfare generally shorter.
Pretty impossible, but my shot at the idea of a perfect game. Multiplayer is optional, but I think it would simulate the idea of a grand staff better.