I'm thinking: an open ended sci-fi RPG in the style of Morrowind or Oblivion, only the game evolves as you play. Let me clarify what I mean:

Each race/faction on the planet has a city. Its so well defended it can't be captured, but the rest of the planet is fair game.

Imagine if you were playing an RPG like Oblivion, and from time to time as you walked a certain road you saw people from one of the cities building a village, or castle, completely of their own free will. Maybe they want to control the road, or maybe there are resources nearby that will help them build more advanced weapons.

Now, say another city declares war on the builders. Next time you walk that road you might see troops clashing with each other, or the buildings in flames. Perhaps there are smaller neutral cities which can be captured and fought over, but not destroyed. Then you could have street fighting.

In the background, another game is running, like a game of civilization perhaps. While a faction can't be totally defeated, another force may become so dominant, that they control most of the world. Then the other races might send spies or messengers and form an alliance. Working as one they might smash the biggest faction until the balance of power is restored. But then the alliance crumbles.

Add to this, some kind of genetic infestation, and alien mutants and bizarre creatures stalking the landscape in more remote areas, or carnivorous plants waiting to trap you.

Other events could shake things up a bit. Pirates? What if you were taking a shuttle from one city to another and it was shot down. You find yourself in the middle of nowhere, looking for food and water to survive while you wait for rescue. Or you could try to make it to your destination on your own, with monsters trying to eat you.

I won't say I'd kill for this game to be made, but it would certainly be awesome. I know its ambitious, but games like Daggerfall and Morrowind were ambitious once. Its only a matter of time... mark my words!