This might’ve been too much like the Dagobah Cave vision, but this would’ve been a cool visual to see during the dark Rey vision. I felt like the vision needed some kind of angle. When Luke fought Vader in his vision and it revealed his own face, it hinted both at the darkness within himself, but also foreshadow Luke and Vader’s connection.
Rey’s vision, on the other hand, doesn’t feel like it has any subtext beyond her confronting her inner dark side.
EDIT: To add onto this idea, maybe when Dark Rey’s fangs come out, you could an additional effect to help foreshadow Palpatine possessing Rey. For example, maybe Rey’s eyes could simply go completely white, or yellow, like Palpatine’s. Even further, it would be interesting if Rey’s face could morph into Palpatine’s at the last minute. It would almost be like a reversal of the Dagobah cave. Vader becomes Luke. Rey becomes Palpatine.