Mindjammer would do very well for the Culture in RPGs - to the extent it barely needs something more specific. It already has sentient starships (albeit on a smaller scale), avatars, and quasi-benevolent interference with other human societies. And whenever I've run it at a convention, I've always included a sentient starship PC option, because surely someone wants to play that.
Though a licensed Culture RPG I'd snap up. Now I want to run Mindjammer again.
The Tripod version 2 is in layout and should be out soon. It's a nice tidy up and simplification of an already simple system. 2e based on lots more play and some new ideas. Still recognisably Wordplay but smoother and quicker.