So, I started out with the notion of making a 5th edition Scifi game. This was spurred by the idea of exploring what you can do with the 5th edition system framework. All fun and games, until you realize how much work it can be. Oh well, we continue the madness.
The problems with setting
The question of game design is one of experience. What stories are the players going to have here? What experiences do you want them to have? The original role-playing games, proto-D&D and its ilk, were extensions of war games. They were changed because the players wanted a different experience from what they were finding in the wargames. The rules grew out of that desire for a new experience.