Your class story quest will not be touched, its just imperial + republic story line advancement they said.
Imo its a half-(donkey+horse) job on an expansion that was originaly ment to be a big patch; considering its only 1 planet there adding.
But, I'd assume there adding alot more cartel stuff! With much harder randomization for the better stuff
+ Not that i care for it but i've heard people wanted this. There adding a gay type relationship quest into next xpac, but from the rumors I heard its just a random npc u basically just flirt with.
That's all ive read or caught while i skimned over stuff @ work.