See, Warhammer: Invasion is different because - if I understand correctly - there are "light" and "dark" factions so even though you have 6 factions or so, it still comes down to one good player vs. one evil player because you can combine light factions or combine dark factions. I think the Star Wars galaxy is too much of a melting pot to have racial factions, so we can rule that out. What we're left with is multiple eras where two primary factions face off. At most, you could have 3 factions, I think (New Republic, Imperial Remnant, Yuuzhan Vong OR Old Republic, Sith Empire, Mandalorian OR Rebels, Imperials, Hutts), but it really simplifies it to just say "good guys" and "bad guys" or as it is more commonly referred to, "light" and "dark."
I think what MarthWMaster was really saying is that they could produce 4 factions, Rebel, Imperial, Republic, and Separatist, but Rebel decks could only face Imperial decks and Separatist decks could only face Republic decks. I think that's certainly an option, but I don't think it will come to fruition in the end. It's almost like creating, selling, and buying two games in one package, since about 50% of the cards couldn't interact with the other 50%. (I say "about 50%" because I'm sure there would be "dark" and "light" cards that could be used in two different factions.) You could even expand it further by adding a Sith Empire vs. Old Republic era. But my question would be how you would deal with the different eras in a tournament. Would each opponent have to play six games (one with each deck) to see who advances to the next round? That seems exhausting. Or would you only get one shot at each opponent and one opponent picks the era while the other gets to choose the factions? Also, the more factions you add, the more watered down your expansions get. If you're primarily an Imperial player, you may only get 5 new cards in each pack (though I suppose it's not so different from LotR and you run into the same problem with the other LCGs).
Throughout this discussion, I can't stop thinking about the Star Wars Miniatures game from Wizards of the Coast. There were optional rules for era-specific battles, but otherwise you could have Luke Skywalker take down Naga Sadow -- and they really advertised that aspect of the game. It was fun, but I don't want to see the same faction system repeated in this game. I'd like to see something new (a tall order, I know, since so much has already been done).
, but this approach is already working for Netrunner - so maybe one day . . . . .