I like the idea of having a seperate "Jedi" and "Sith" class for the force users.
Or perhaps you could even go farther and have "force sensitive" versions of other classes (ie: they have weak force powers and weapon skills, much like the classes in MotS).
The Sith of course could be like what was planned for Obi-Wan. They could make use of double-sabers and focus on dark side powers.
Light Jedi of course would use the normal saber and light side abilities, and Dark Jedi could use dark side powers, but would use the normal saber. Perhaps they could be balanced with some neutral powers and weaker dark side abilities than pure Sith, etc.
This is all for multiplayer of course, since we know that you're going to be focused on Light Side in JK2 and you won't get to choose your side (all the powers being "grayside").