Maybe the Nihilus vs Atris cutscene could have something to do with him not killing her on Katarr, and wanting revenge or something? I'm not entirely sure if that would fit with the story as I too haven't played in a while. Also, I'm not sure how Atris would stand against Nihilus, since he can seem to be able to drain the force from an entire planet.
Still, I would for such a scene to be included.
As for captioning Darth Nihilus, you'd have to be careful with that. Part of his menace as a villain was that you didn't understand him, but knew what he was saying was very "evil" (for lack of a better word.). If you wrote dialogue for him you'd have to make sure it's apt for a planet-killing, barely human Sith monster.