I am probably in the minority and this may not be doable with the source material, but to me, in the first two movies Rey is a character with a “default” star wars background character… background. Parents either poor as shit, or dead for trivial reasons (disease/gang violence/whatever), or abandoned/sold her (or… all of the above). Such is the star wars world (except on more sophisticated worlds like naboo or alderaan where you might have more “normal” parents). And her specialness comes not from her origin, but from… the force awakening inside her for some reason and her having a good heart or whatever.
As such, a “reveal” post-TLJ about her actual origin - any reveal - diminishes that in my view. If her background is in some way special, and Kylo Ren or whoever reveals that to her, that gives her character motivation basically for free.
If she is a Palpatine, she has an innate reason to fight against her legacy, to basically cleanse her name in some way, so as to show herself not to be what her ancestry would suggest her to be (although that is also undermined by her parents being good and loving already). If Palpatine killed her parents it becomes a simple revenge story, in the end she takes her revenge against him and all is good (even though apparently that’s what he wants anyway at the start, but at some point that just changes…? and he wants her dead?). If she herself killed her parents it’s again sort of a self-redemption story and she has newfound purpose with the reveal. If the reveal is that there is no reveal - no “free” character motivation - then she has to find her place in the story herself and has to wrestle her inner demons that she has anyway - dark origin or not.