I was playing around with the browser-game
Ikariam and giving this scenario a little thought.
Anyway, I think a Greek mod would work really well if based on its own archipelago-like random-map. Give it a good tech-tree and diplomacy options - such as the aforementioned system of colonies and vassals - and it could make for a great multi-player game.
Some ideas:
The ability to build new cities (rather than just have one), but attach certain actions to the palace, so your new cities are in a way handicapped and can't compare to your starter city.
Generic leaders with relevant traits - rather than a named leader, you would have options like "the General", "the Philosopher", "the Imperialist". Could make artwork a lot easier too, just use Alexander, Caesar, Augustus, Pericles, Hannibal and maybe Cyrus, among others.
The most interesting task could be implementing some system for politics, taking a look at the various forms from democracy to monarchy or dictatorship that existed back then. The Civics screen could have some great options there.