I've been contemplating the traditional 4X style game as of late; games like Stars!, Master of Orion, Civ4 and to some extent the RTS-hybrid Sins of a Solar Empire and Age of Empires. Most of these games seem to boil down to the same basic model - you start with a single lone colony (settlement, city, planet, colony, whatever), expand the colony, send out scouts, establish more colonies, build up your armies and finally engage in some way with other AI or player factions through diplomacy or warfare. In all of these games you're cast as the head of the empire, you have to manage everything from colony growth, expansion, war, diplomacy - as your empire grows, so does the number of tasks you have to work through. Responsibility, however, stays pretty much the same throughout the game. Aside from volume, the game itself stays pretty much the same at the start as it does the end.
What I've been pondering is how such a game would work out if you, the player, were cast in a different role that itself changed as the game progressed. What if you started out as some low-level city planner, being given direction and a budget by an AI emperor who was responsible for the entire empire. You, as the player, would grow your individual colony and engage in politics within your empire to acquire new resources or try for promotion. Promotion, then, would move you up and in charge of an area of colonies - except instead of being able to command them in a low level, you took on a role that became more strategic, telling the governors of the colonies where they should focus their efforts. You could hire and fire new governors depending on performance - of course, you are still ultimately accountable to the levels of government above you.
I imagine that politics would start coming into play and you could choose to ally yourself with certain factions within the governments - outcomes could be wars within the empire as people try and oust you, or even a general coup against the government which could see you rising to higher powers. As the game progresses, you take more hands off and strategic control of the empire and have to deal with political issues outside of your empire - joining and forming galactic alliances, or committing resources to coalitions of other empires to remove or destroy powers that your allies don't agree with.
The longer the game goes on, the more control you gain over the empire, but the less hands on you become with individual planets and colonies.
The most important thing of course is to make sure it's fun, and it's so hard to tell if something is going to be fun until your actually playing it. I'd be interested to see how you expand this idea (or any other ideas for that matter).