My thoughts on interstellar travel in KSP: Why can't we have a procedurally generated galaxy with billions of star systems orbiting a central black hole? The game has no need to simulate all of the star systems all of the time; it only needs to simulate the system containing the ship with the current focus, and when a previously visited system is revisited (either by travel of a ship or switching focus), the positions of the planets can be updated depending on the time elapsed since the last visit. To reduce the number of stars being tracked for the purpose of interstellar SOI changes, divide the galaxy into cubes (10ly x 10ly x 10ly perhaps? that'll need tuning). Actively track stars in a ship's current and neighbouring cubes, schedule tracking upgrades, tracking downgrades, and night sky apparent magnitude changes for other stars whose orbits cross the ship's current and neighbouring cubes, and perform a full recalculation on a background thread as a ship itself approaches the boundary of a cube (a very infrequent event). To make sub-light interstellar travel interesting without making interplanetary travel trivial, add high TWR high ISP engines, but put them at the far future end of a tech tree in career mode, and restrict parts in sandbox mode to those that have been unlocked in career mode. Also, to use such an engine for interstellar travel, you'd have to use a brachistichrone instead of a transfer orbit, so the engine's usefulness for interplanetary travel could be further restricted by having the navigational aids for brachistochrones display interstellar SOI changes only.