Well I would imaging a couple scenarios immediately that I could make use of as a developer.
The big one would be adding,editing,deleting objects to a simulation via code and setting simulation parameters programmatically.
Another would be writing custom even handlers to do things on say a planetary collision event, an objects settings change, etc.
Adding custom rendering handlers...so I could add custom rendering piece of code that could draw say disk with some opacity that trails behind a planet or objects orbit on it's orbital plane to more clearly show it's plane of orbit in the simulation, (for example).
The basic ability to do those things for starters would open up a whole bunch of possibilities.