While I know this will NEVER happen I do think if Bioware really wanted to add a thrid faction it could be done relatively soon. I would argue that a Hutt faction would make the most sense (lots of credits to lure people with weak loyalties in). A Hutt faction seems like it wouldn't be a lore problem like a faction of mandos would be. Ok the following list is how I think it could be done.
*No new classes, both republic and empire classes would be allowed to join the 3rd faction.
*The option to join the 3rd faction comes at lvl 50 after completing your class quest series. This would mean that Bioware would not need to add new content from the ground up. Obviously this would be a hole in their story pillar (basicly at level 50 you get the option to leave your faction and join the Hutts. Maybe a short quest series to make the change offical, nothing major).
*A third faction main space station or home world would need to be created.
Obviously this idea is not perfect, but if Bioware was serious (I don't think they are, or ever will be) it is not as big an undertaking as people are making it sound.
