The problem with sci-fi is that there's very little common ground. With fantasy, there's a sort of baseline based on Tolkien and D&D, plus of course the common understanding and misunderstanding of the medieval/early renaissance past, to the point where you can say "This is fantasy, but our orcs are smart." I mean sure, fantasy is in theory an extremely wide concept, but the pseudomedieval Tolkien/D&D makes for an extremely strong magnet for the word.If fantasy as a dominant genre fell away then sci-fi would probably be next in terms of mass appeal? Supers seem to be a bit tapped out at present, and horror scratches a different itch than fantasy / sci-fi in terms of power fantasies or lack-there-of. So maybe Starfinder or Traveller?
But science-fiction is a much broader idea. Are we talking Star Trek? Star Wars? The Expanse? Dune? The Foundation? 2001? The Fifth Element? Fallout? These are all very different properties with different levels of wundertech and magic. This all makes it hard to make a "generic" science fiction game that doesn't turn into a game creation kit like GURPS or Savage Worlds (with Savage Worlds being significantly closer to play out of the box but still requiring a whole lot of choices before you get started). So I think the Starfinder route is probably the best for a semi-generic sci-fi game: create an actual setting with a lot of variety, and make the baseline essentially a non-supers Guardians of the Galaxy.






