An open world MMO seems out of the question.
However, it would be interesting if there was a story mode to immerse players into the world of GOIO. Would be nice to have a town or base to land the ship - walk around, interact with stuff, accept missions from NPCs or bulletin boards. Completing them can earn you money for outfitting (e.g. more armor, engine thrust, higher weapon grade); unlock missions, ships, weapons; better crew (AI); rank up in your faction etc.