If i where dev i would, add the whole galaxy to kerbal space program. I would also add creatures and add biology research, liquid research, Build in space to extend a existing space station. A more sci-fi throttle back system to be optional though. A AI system to have AI flight into space for nice views from space stations as AI comes in closer to dock with the space station to bring supplies up there. A IVA view of space stations. Huge star-ships wich you can walk around in sleep in and eat. Asterioids, Comets. A Build in space for lager space crafts. Forcefield's. Aliens to have a diplomacy, trade routes. Enemy's to Fight. With the new tech tree i would say you start with in 1960 apollo tech era up to star trek type tech and maybe so on. And the list goes on and on and on forever.
