Okay, so I'm still trying to come up with a concept for a science fiction game I'd actually be excited to run. I recently bought Dungeon World and found the game mechanics very interesting. Today I bought the original game, Apocalypse World, and started into it. I'm finding I like the fresh take on gaming that the Powered by the Apocalypse games all seem to have. Too many games out now are either later editions of "original" games or retro-renaissance retreads of one of those games.
Two campaign concepts which I think would work for a sci-fi campaign are either a Battlestar Galactica type game where a small fleet travels around fleeing and/or exploring or a space scavengers sort of game where they explore and loot their way through the dangerous locations of a devastated galaxy (basically a sci-fi take on dungeon crawls). As I read through AW I noticed that a couple of the playbooks (character classes) include a set of followers for the character. As first I thought it would be awkward to include a large community of NPCs but quickly realized it was perfect for a "wandering ragtag fleet" based game. For instance, each player with a Hardholder character could design a ship which is home to their community, and each Chopper one for their gang. A Maestro'd or Hocus character might have their own ship or be housed on another charancter's ship. Or you could include one big main ship, maybe a former luxury space liner, with everyone on board in their own "neighborhood". The Mad Max type post-apocalypse background setting of AW also contains a streak of psychic weirdness. This lends itself well to a space scavenger game set in an area of space ravaged in the fairly recent past by some event which left behind things of horror and wonder.