Rey Palpatine?
Rey’s identity is by far the most tangled web of confusion in the story, so disentangling them starts with determining the overlap between what is possible and what is thematically resonant. The most resonant part of Rey’s identity is that she was a nobody abandoned by her parents. However, this is not sufficient because it merely says what Rey is not: she is not a Palpatine, not a Skywalker, not anyone of any importance. TLJ establishes that her insecurity and grief over her abandonment drives her actions, and her deepest desire is to find a family to call her own.
Therefore, if the story of TROS is to remain relatively intact, the most promising tactic would be to establish that Rey’s Palpatine heritage is a lie created by Palpatine in order to tempt her with the one thing she desires most: belonging. This is easily done. The only object tying Rey to the Sith is that Ochi’s ship appears similar to one that left Jakku with her parents many years ago. However, the solution to this puzzle is staring us in the face: They are simply different ships. This is demonstrably true by comparing TFA’s vision with Rey’s memory in TROS, where the designs of the ships are quite clearly different. Palpatine can latch onto this similarity and tell Kylo Ren the lie that Rey is a Palpatine, and he can convey this to Rey. There is also dialogue between Finn and Poe where they discuss the information in D-O that appears to confirm the Rey Palpatine connection, but that can be deleted.
Rey Nobody
Now that Rey Palpatine is established as a lie, a problem arises. There still needs to be some dark revelation about Rey for her to doubt herself, beyond the Rey Palpatine lie. This is because all Rey needs to do is reject the lie in order to resolve the problem, which isn’t thematically resonant. This was the problem in TLJ as well: if Rey is a nobody, it isn’t particularly devastating. Rather, the film establishes that she is a force of light to rival Kylo’s force of darkness, as described by Snoke, so by rejecting Kylo’s hand she is establishing herself as good in opposition to Kylo’s evil. This can be viewed as a victory, rather than an insurmountable obstacle.
Dark Revelation
Any revelation about Rey must be about Rey herself, rather than her lineage, and must cast her story into doubt. The strongest way to do this is to flip the script and paint her as an underdog in her own story, a force of evil rather than one of light. This is what TROS attempts to do with Rey Palpatine. Yet the issue, among others, is that it is established that Rey is Kylo’s rival in the Force, a counterbalance to an equation of light and dark.
The solution now appears obvious: Kylo Ren must be a force of good. Is there evidence for this? Yes, in fact. He is secretly drawn to the light, and all characters know how conflicted he appears. It takes only a little more exposition to establish that he has secretly been attempting to destroy the Sith for his entire life, ever since he learned of Palpatine during his training with Luke. In order to get close to Snoke, Han had to die. In order to find Palpatine, Snoke had to be destroyed. Ben followed the ways of the Jedi, divesting himself of attachments to all those whom he was afraid to lose and forging a new identity for himself as Kylo Ren, a false identity taken merely to complete what Vader could not and destroy the Sith once and for all.
Rey’s Darkness
Kylo can reveal to Rey the truth, that she was always driven by the Dark Side. Her insecurity and need for a family is founded on selfishness, which is the core of the Dark Side. She wears a mask just as Ben does, but instead of an evil visage she wears a mask of false benevolence. Deep down, she is driven by a desire for a family, and Palpatine’s lie secretly appeals to her because it allows her a belonging that she has never allowed herself to feel with Luke or Leia or her friends.
Rey’s blazing fast rise in power is only possible through the use of the Dark Side, giving her a quick and easy path to a place in the story and the family she has always wanted. She knows, however, that only Palpatine would really accept her, and so Kylo reveals to her in the hangar that though she may not be a Palpatine, she undoubtedly has the spirit of a Sith. This is why she is unable to contact the spirits of the Jedi.