I think in KOTOR III the bigest bad guy should be a Subtle Betrayer like Sidious
and he should be more powerfull than you can become during the game... (you
shouldn't be able to kill or defeat him...)
If you go to lightside you should survive at best and if you go to darkside you
should become his apprentice
And the game should have very dark ending no matter which side you choose
to go to... By the end of the game there should be no more republic...