It would be very cool to have a binary black hole system somewhere in the solar-system. I.e. two black holes in a tight orbit around each other at very high orbital velocities. This could allow for very powerful slingshots to bring probes to interstellar speeds.
If you have the energy to get to black holes rotating around each other, you probably can build ships that don't need to slingshot. 'Cept perhaps for braking maneuvers.
