What KotOR 3 can benefit from is independence. Independence to pick if you want to work for the Sith or the Jedi, or work alone. A "Storyline" would be that the protagonist is helping rebuild the Republic and squash remnant Mandalorians/Sith/Dark Jedi when he stumbles upon The Star Maps and reaches the Unknown Planet, gathering immense information on the Rakata. The Elders tell him that their rivals, a group of powerful force adepts have set forth to find a device powerful enough to disintegrate an entire planet (read: Death Star).
Our usual Jedi dude also finds Sith remnants who want to use his high force potential to "destroy" the Republic. The hero is free to choose wether he wants to be a Jedi Master, a Sith Lord or something completely different. He chases the Rakata as they travel to the outer reaches of the galaxy and on the way he helps the Jedi rebuild and such, though he never tells his secret mission to the council.
Finding the Rakata will be tough and the game will not hold the player's hand and guide him around. He will have to analyse information, see what's best for himself or others and do what he feels is right. At the end, when he catches up with the Rakata, he learns that the Sith remnant are after the Death Star too and so are the Mandalorians. The player is thrown into a literal race with the other factions as he seeks to obtain the device. He learns that the device doesn't exist, but only the plans of it do. The ending will depend entirely onto the player, wether he wants to secure the plans for the Republic, the Mandalorains, the Sith, whatever.