I'm pretty fond of the idea of playing with physics. I feel like so many games touch on physics or play at implementing physics however orbital physics is a true challenge to fly and use. Even just exploring the use of orbital mechanics to sling shot or decelerate from extreme speeds on the approach to a solar system could be pretty exciting. What types of thrust and ways of moving through space and time have you been thinking of exploring?
The super complicated thrust based control system of Star Citizen is very impressive though I think it's a bit of an engineers wet dream more so then a players. Since for the player all it really means is figuring out the limitations it presents. I'm not sure what types of controls your game would present to the player to navigate the universe but I would seriously mull over the ways the player could/would do this as this represents the way your player connects with your presentation and is the way the player expresses and communicates their feelings about the experience which can even be deciding factor on the directions the game takes as you prototype the project.