Custom solar systems with universe sandbox?,

@Kell - personally I would like the benefit of better plausibility of fictional solar systems. US² can help a designer find planet compositions, atmosphere compositions, temperatures, and orbit parameters that are self-consistent. First, I think there's an educational benefit to exploring more realistic planets building. Second, as a player I think there's a benefit to planning a mission for a planet by making guesses about the destination based on real phenomena.
I think the US² output is already in an open json format, so there may not be any changes needed on the US² side. And writing an importer for SR2 might be straightforward.

A planet builder is planned though.

This will require significant effort from both developing teams and has little benefits.