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(Updated with the official website link)
Dulfy's posted some great info on the new expansion. (Largely the same stuff as MikeB did here, but with a couple of new images to go with it.)
You know, the expansion's giving me the idea that this is Bioware's version of a clean slate, hence the whole starting at level 60 thing.
"A man can have anything… If he’s willing to sacrifice everything. Step into an epic story-driven adventure as your character becomes The Outlander, a veteran of the Great Galactic War. A third faction threatens the galaxy as we know it, and your choices will determine the fate of both the Sith Empire and Galactic Republic. Knights of the Fallen Empire includes the first nine chapters, fueled by BioWare-style cinematic storytelling, that kicks off a new player-driven story arc that puts you at the center of a conflict where your choices have impact on outcomes including unexpected twists and betrayals. Choose your path…join or betray companions, old and new…and shape the future of the entire galaxy as well as your own. Best of all, this is only the beginning…"
It also seems like a great deal will be changing judging on that line about betraying companions "old and new". Maybe they're scrapping the unpopular ones that no one uses, and focusing on the popular ones going forth. (They've already done this with SoR to a large degree, where only people's favorites companions got new dialogue, while some like Skadge got skipped completely.)
I'm also guessing there will be a chance to revisit your existing romance, à la Mass Effect 2 and 3.