Dark Rey?

There was a conversation she had with Finn where she said she had seen herself on a throne with Kylo Ren. " I'm afraid no-one knows who I am " she told him. She was scared she might go to the Dark Side I think was the implication. So they were half-heartedly trying to have their cake ( Good Rey ) and eat it too ( Evil Rey ).

That would be a possibility, but even then, I think it’s clear from the beginning that she’s not going to stay evil, because you wouldn’t do that with THIS character. Not in this franchise. These hints in the trailer remind me a bit of the cliffhangers in the old Batman series, where Batman was trapped and the narrator said something like “Will Batman escape the trap? Will the evil Joker triumph forever? Don’t miss the next episode!” Even then, you always knew that the producers wouldn’t just let Batman die, except that in that show, of course, the narrator’s words were meant to be funny. With the Star Wars trailer, on the other hand, there’s a serious pretense that Rey might turn to the dark side for good.

I recently saw the movie The Stepford Wives (1975), and that movie doesn’t have a good ending – you suspect it’s going to end well, but you still don’t know how it’s going to end as a viewer.
With a movie like The Fearless Vampire Killers, you think you know it’s going to end well because you’ve seen it in numerous Hammer Studios movies – and then you’re surprised with an unexpected ending.
But with the Star Wars movies, I know beforehand that they’re going to end well. Movies like the two I just mentioned are more artistically free, and they weren’t made by marketing strategists who don’t allow for creative experimentation. They’re not thinking, “What unexpected things could happen to Rey? “ but, “Well, this character is so popular, there are Rey action figures, Rey costumes, etc., and the audience wouldn’t like Star Wars if this character suddenly became evil and STAYED evil.”