I think they could start with Bastila or Mandalore, but they better have some awesome plot storylines/twists. The plot and the mystery and the history is what made Kotor I so good. The star maps and Rakata mystery were really tantilizing and kept me playing well into the night. Kotor II had a decent plot, but not as compelling or grand. Kotor III should have Exile or Bastila etc finding REvan trying to start a revolution among the "true " sith. So they help him.
I think that they can make Bastila and Exile at least partially customizable in two ways.
1. Start out specifying ds ls or neither and whether bastila or exile are guardian/consular or whatever. Most people decide at the beginning of the game what they want to be during this go around.
2. create new and awesome force powers that only Master Jedi can get, like teleportation, illusion (creating extra "you's"), force turn (making someone turn to light or dark side), weapon strip (suck their lightsaber or gun out of their hand) etc.