I think a great addition to the game in the future would be the ability to construct larger ships using an in-orbit construction yard. In career mode, it would require supplies to be brought up from the KSC in order to continue running. This space construction yard would build ships 5-15x the size of what can be constructed at the KSC VAB, containing extremely advanced futuristic parts designed to take kerbals to other solar or even star systems so far away that their gravitational influence on the kerbal system is nil. Reaching these systems would take great amounts of planning and maybe even a galactic map feature would be needed too. Alright, im getting a bit carried away. Obviously this is very far out because it would not work until docking, career mode and more planets/stars have been implemented, but I feel like if this was ever added to KSP it would increase the novelty of the game 100fold.