There's got to be romance!!! It was GREAT in KOTOR I with Revan/Bastila Revan/Carth!!! But I also like the aspect of choosing who the character can be with like in KOTOR II. Of course, in KOTOR II the romance was too subtle and there was no outcome to it.
There's got to be a pregnant jedi too!!! It would create a lot of conflict and that'd be GREAT!!! Perhaps the pregnant one could be the PC's sister or friend?
There has to be an in depth plot with A LOT of sidequests and a lot of interactions between characters in the game.
The new game should be called KOTOR III: The lost jedi. In the end of KOTOR II, Kreia reveals that the NPC's that could become Jedi are the lost jedi. Maybe they will have to be rescued... they'd join the party. (Mira, Disciple, Handmaiden, Bao-Dur, Visas Marr) and they are all neutral again since the exile left.
The plot should be to first rescue the Lost Jedi, then go to the unknown regions and fight the "true sith". The first part would be where the PC gets most of it's levels. The second part would be more intense and everything comes together...