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.
lol well for Revan and the Exile - I see no reason why you should see their faces; Revan has his cool mask from the first game and the Exile stole Nihilus's after kicking the crap outta him, so they could cover themselves with them. As for my idea, it was only very basic for the beginning of KotOR III...I have no major ideas for the rest of the game, although I do think that Kriea's ghost should appear in it.