now, ive been reading through here and noone seems to have realised that 99% of the promotional work was done on Nihilus. (forgive me if someone has said somthing like this - i only got past page 5). so you would naturally expect him to be the main bad guy and be the big finale, rather than just a side character with no real input into the game.
and i thought - what if the game finished when bastila walked in after carth sent you off to find revan? that'd give it a kind of ESB-esque cliffhanger ending, and your not left with any "well what about this and what about that" thoughts and lots of loose ends, and you'd know that a sequel was coming to explain what happens next.