The following factions are player-backed:
New Republic
Sith Empire
The Mandalorians
Imperial Remnant (potentially someone will actually play as Thrawn, which could be exciting)
Coporate Sector Authority
Hutt Empire
Trade Federation (new and improved, with no more droids)
Hapan Star Consortium
So basically a full house. Although to be realistic... and not to discourage anyone. "Active" participation usually drops to 2/3rds of what we start out with. Sometimes running a faction can be time consuming, so if you'd prefer a more peripheral SL-only role, or one of NPC support, I'd be more than willing to find a spot for you!!
The general theme of the galactic battleground will likely be a large-scale outer rim focused conflict, with only the more traditional factions vying for Core control.
Also, a great deal of canon characters will die in the Battle of Coruscant, so essentially we are making a full departure from where previous sims have ventured. Now that JJ Abrams has carte blache to rewrite canon, all of us can throw the books out the window.