So, just an idea I'm brainstorming right now: A crew of space mercenaries/pirates, mostly Chaotic Good-(ish), set very VERY VERY far in the future (roughly 2.2 billion years in the future, give or take; it's not really specific). The basic idea is that our solar system has been gone for quite some time, and universally, the lights will go out for good at some point in the next million years or so.
The crew of the ship is a ragtag band of misfits, who chose to work together for some reason. The catch? Not a one of them are human. Their "powers" are just abilities that are indigenous to their species. Other than that, they tend to wear a Survival Harness (communicator/Universal Translator/Enviro-Adaptor), and carry a weapon or two with them. Essentially, picture a cross between the Jonni Future series and the Starjammers (the setting is very pulp-inspired).
And yes, humanity does still exist in this era, but they're scattered all over the place; they're just not in the spotlight any longer. Do you think it would be possible to play an all-alien crew without a Token Human? Or does this sort of idea need a human for the "audience" to relate to?