Both previous rule-systems were pretty spiffy and worthy of revival in their own right, but I think that Poseidon would make a great background for Traveller. Unusually for the settings mentioned as possible Trav settings, interstellar travel is expensive and fairly uncommon. Lots of lush detail about the world's hostile ecosystem, suspicious bio-engineered/ modded first generation "natives", mysterious/ unknowable alien "aborigines", and inter-corporate politics feature. It's a genuinely "political" "cyberpunk" setting.
With lovely 1st edition artwork, please.

Any thoughts?
(PS. I also think that Poseidon would make a great setting for adventures in the Dredd universe: the powers and responsibilities of the GEO Marshals are very "Judge-like".)