...Final Fantasy's been combining medieval fantasy and sci-fi since Final Fantasy 4, and the series is still going strong. Even in the massive multiplayer online 'roll'-playing front, you have titles like Project Entropia, Anarchy Online, and other such sci-fi games. And those seem to get good recognition as well. Hell, Star Wars is basically fantasy meets sci-fi, and how successful is it?
True on all instances.
Still, FF is a respected for it's own worth. For being a good jrpg-series. I wouldn't really call them scifi here, and on the other hand their largest audience is still where the jrpgs's home is at: Japan. Even if the games stopped selling in the western world, Square still would have more than enough buyers back home.
About scifi mmos, they're...well mmorpgs? Both of your examples came out during the huge mmorpg boom, which is still going on. True, they are rpgs in sense and gathered an userbase for just being different from the majority of the other mmos, but we were talking about crpgs, weren't we? (What were those other scifi games you mentioned? I'd like to have examples.)
About SW, the only examples of succesful merging of crpg and SW are KotOR-games. The first one had the reputation of Bioware to back it up. The second is still on the verge of being a huge hit, but when it does cross that line; an argument must be made that a huge part of it's buyers were the original fanbase of KotOR 1, having nothing to do with scifi. On the other hand, a big factor fo their success was also the sensation of new. Which kind of undermines my argument
I really want to be wrong, you know.