Just an idea I'm having while sitting idly waiting for some things to finish... A permanent game, 2-5 minute turns, whoever wants to connect at any time can do so. Score is recorded from the beginning to the end of his session and a difference or ratio is used to measure his success (divided by the number of turns he played or something like that).
Tech upkeep is enabled so that when a nation loses its leader (when he goes offline), it deteriorates so if someone takes it over a few hours later, he gets the room for moving forward again.
Defense units in the capital have brutal defence power and basically can't be destroyed so that no nation is killed and has an opportunity to bounce back when someone takes it over.