- I think it is a space game. Set in the far future. Only fantasy can give you as much freedom ( not period pieces [like westerns], or strict genre pieces [like Toon]) but it risks throwing out all the tropes and archetypes we share in our culture. Assuming we want a ton of options without a cryptic, hyper-personal setting to learn, space is the place.
- System for biological enhancements for players
- System for technological implants and replacements for players
- Genetic engineering
- Martial Arts
- Robots and AI
- Uploading personalities into computers
- Downloading skills and memories
- Software Hacking
- Ship outfitting and combat
- Weapons - lasers, rail guns, flame throwers, radiation weapons, explosives
- Interesting, biologically feasible aliens species. In other words no bipedal, you are the embodiment of a human quality, Klingons. But like starfish-things that replicate through limb loss and pass their memories on to offspring.
- Three layers of space civilization 1) the slow colony ships, some just now reaching planets 2) the near-light speed ships that put passengers in hibernation and 3) the FTL gate culture that found or built gates. Players starting as any one of these cultures would have interesting artifacts to explore and it's easy to grasp-- these people left before us but were much slower etc.
- Light on the historical details. "Who knows how it got this way . . . what do we do now."
- Every planet can have a different flavor, from gritty horror bug hunt to cyberpunk social machinations.
- Time travel
Maybe another tricky aspect is tone. I think you can travel far with the bland, banality of evil that corporations and governments give us. Dark, gritty, and quirky have to be explained with more setting details. Science isn't spooky or weird, it's what people are using it for that bugs us.
The thing that gets my juices going is thinking about how just two or three good aliens could expand the possibilities enormously. If you think about how they would have completely differently designed robots -- why would a starfish-thing make a bipedal robot?-- different weapons, different enhancements, different spaceships-- Sorry, dude you can't fit in the helm. Hell, give one of the species mental powers based on quantum entanglements. I'd be leery of too much magic-like stuff, everything should be explainable even if in psuedo-science-ese. No angels or demons-- either they are alien species or we're playing D&D and just didn't realize it.
In trying to think of some other fat possibility I can only come up with something fantastic that has tons of ways to affect the world: runecasting, psionics, wizards, sorcery-- but that's basically D&D with some house rules tacked on.