It's interesting to think about that Luna and Stella look so much alike, yet Noctis doesn't seem to be put off at all when he meets Stella for the first time? I wonder if this changed somehow and Luna wasn't originally a character back in the Versus XIII days.
While watching the old trailer again, I also noticed that when you look from Stella's perspective, she claims she can see the light, but you don't actually see it, and you only see the light when looking from Noctis' perspectives.
Does this mean, Stella is lying to Noctis in order to become close and familiar with him to then later betray him which is why you see them fighting in the old trailers.
This supports the theory that Stella is actually the Nobody of Luna.
Sorry, I had to do it.