As far as Linux goes, a good first step might be getting Orbiter to compile under winelib.
As far as UI/maneuver nodes, etc, for vessels that do not emulate the avionics of a specific real (or fictional) spacecraft, and thus would be dependent on MFDs in classical orbiter, it might be good to have a modernized MFD mechanism, on which a new set of standard navigational MFDs could be built (including perhaps something implementing KSP-style maneuver nodes). The fixed number of side buttons on MFDs is somewhat limiting, having "touchscreens" as the basic spacecraft UI element might give more flexibility. The legacy MFD system would need to be kept for back compatibility. Development time allowing, I suppose you could implement a third UI style: "DSKY", meant for 60s-era spacecraft (or spacecraft fitting that aesthetic), but not implementing their own avionics (as NASSP does). This would mostly be for flavor, rather than usefulness: retrofuturistic addons (for example, Space Odyssey inspired) might favor the use of an even-sparser UI than classic MFDs.
As for Orbiter vs. KSP, the small size of the remaining community, etc, it somewhat strikes me that Orbiter is almost an engine in want of a game. The remaining community seems fairly addon-developer-heavy, and maybe the best thing is to position Orbiter as a general space-sim engine upon which more specific projects could be built, maybe with a couple proofs-of-concept.