I'd like to see nations based on Empire of the Petal Throne (Tekumel) or Talislanta, both of those are very original fantasy role playing settings/games that include elements of science fiction, without going completely overboard into B movie land.
That said, I'd really like to see a couple Ice Pirate units show up in the game someday
Star Wars, Buck Rogers, etc. might be far better known, but the process of translating those "universes" into Nations would be much more of a matter of shoehorning than the two I mentioned, each of which has a very long history and a rich, complex setting to draw from-they're also both woefully underrepresented and relatively unknown.
HTTP://WWW.TEKUMEL.COM/
http://en.wikipedia.org/wiki/Talislanta