I'd like to see Ossus in the game, well the ruins of. maybe there could be storylines involving Odan-Urr who still resides there in tree form, or the group of jedi survivers who hid in a cave during the planets near destruction.
Coruscant, speaks for its self.
Corellia, like onderon has populated moons, also corellians were enslaved to build the star forge
Arkania, originally a sith world, later under the control of the republic. there was a jedi praxeum there at some point.
It all depends when the game will be based, the sith (exar and Ulic, Revan and malak) pretty much layed waste to most planets in this era. maybe if the game was a prequal to kotor 1 places like ossus would be more ripe for stories