Space Opera was an old rpg that basically had expies of elements of various science fiction franchises. So it had for instance equivalents of the Federation from Star Trek, various races, etc. I've been thinking, since homebrewers don't need to worry about copyright, why not have an rpg that includes the actual science fiction franchises crossed over? I figure either Age of Rebellion/Edge of the Empire would probably work very well.
The main problem would be creating all of the various ships and such that would be necessary to play the campaign. Especially since there might be some disagreement on how various things compare in power (see the Star Trek vs Star Wars debates). Part of solving this problem might be to focus on some specific area to start with and then expand. Perhaps Ferenginar and the nearby space might be a good place to start an "Edge of the Empire" campaign. Or perhaps put it near some sort of enclave of Imperial control within the Milky Way galaxy, which I think might be on the other side of the Klingon Empire from the Federation in the Beta Quadrant.