Perhaps. I write plotlines myself now and then. What I would advise you is that you do keep Revan and the Exile in the game. Killing them off is to cheap and also, you should be able to tell the game who Revan and the Exile were in terms of Gender / Alignment. You should also be able to select their faces. Those are top priorities.
Furthermore, your should think about what happened to the party members of Revan and the Exile. Do the party members of the Exile form a new Jedi Council? What if the Exile is DS?
I see that you start off as a Jedi on a refugee ship. It's good that you do have a lightsaber at the start. What I wonder, maybe you will explain it later but how did you stay undetected during say, the Shadow War. Why weren't you discovered by Darth Sion / Nihilus or Kreia?
Hard task? No, it can all be done. And before you wonder if it is difficult to select a face for Revan and the Exile in game, consider that you were able to select the model and color of your lightsaber in Kotor II before you stab it in the stone on Coruscant. A face for Revan and the Exile is exactly the same, they are just game objects.
That's exactly what I've been thinking hawk.
To keep it the way that the player had wanted it or played it since they bought the other two games, the developers are going to have to let us choose what happened. For instance, you get to decide what happened to the people via dialogue and the game will begin to make the necessary changes to make it LS or DS based on what you said through the main character. You could easily pick a face from a simple questionnaire the game will throw at you like it did in the other two games before. As hawk said, it's not hard at all.
Speaking of the main character, it should be someone else. I don't want to play as the Exile or Revan again. They'd be too powerful (it would just be bad if they got knocked out and lost all their powers again) and it just wouldn't make sense as they would be in the Unknown Regions and that would be a conflict. Besides that, it would just be boring to be those characters again.
So, a whole new character is needed to end this, make it a trilogy, which SW is known for anyways. So, we end the game with a trilogy and we get to complete the series with three, different main characters.
I like your idea, hawk. And those are very good questions. Or maybe the person is a late-comer to the Force, or something like that.