Kashyyyk - Czerka makes for a good and functional antagonist for both factions.
Dxun - A planet (moon) full of monsterous beasties,at least one dark side ruin, and remanents of the Mandolorian war. Would make a good end game addition.
Dantooine - Continuing the "what happened after" from the KoTOR games.
Manaan - Continuing the "what happened after" from the KoTOR games.