There could be some sort of morale bonus for taking Coruscant, or maybe a detailed, interactive campaign based on the Thrawn trilogy, the way EaW was for the Death Star. Events take place and such as they do in the books, but the player gets to play through it. Perhaps you come up with an original hero, and make a new story? Regardless of story, a scenario in which some is MacDuffin on an enemy planet, and the player should go raid the planet would not be unfeasible. Maybe there is some (extremely nerfed) version of a star forge (or similarly valuable resource), and the scenario hinges on holding it? At any rate, the possibilities are nearly limited, and I am sure you will do well.