What functionality is missing? What is unsatisfying with the current situation?

Perhaps this is unique to me, I suppose we will see. I wanted to have two calendars, where in-between these calendars a celestial event causes my world to start orbiting a different celestial object. I would love for there to be an option to select whether a celestial object is orbiting your world, OR whether your world is orbiting IT, and which celestial object(s) your world is orbiting. The standard option assumes a celestial object is in orbit around your world.  

How does this feature request address the current situation?

It would enable the option to distinguish clearly between what object(s) the world is (currently) orbiting (a.k.a. one or multiple suns? a black hole? something else entirely made up?) and what objects are orbiting the world. Perhaps even add an extra feature of how the positioning of the world, relative to a celestial object it is orbiting, influences the seasons.  

What are other uses for this feature request?

It adds the benefit of customizing i.e. your sun, just as you can customize the name and appearance of moons.