I’m still pretty sure Palpatine was just himself throughout all of his life. Essence transfer requires that ritual we saw at the end of TROS. And we all know Palpatine only killed his master in his sleep. That was the whole reason he likely did it - his master wouldn’t have enough time or awareness to even attempt a transfer like that.
Palpatine tells Rey she straight up can’t put an end to the Sith, the way Vader did. Because of her hatred, her anger, if she tried to kill him his spirit would pass unto her. That’s all that’s needed for the essense tranfer, to strike down with hatred. The “ritual” at the end is just a big show for his followers, but it just boils down to Rey killing him with hatred. It makes sense that’s how the Sith spirits would pass down through generations, as their creed is driven by hate, anger and greed, the apprentice is always looking to overthrow the master for their own selfish reasons, only to be consumed and fueled by the anger and greed of all the Sith that came before. I imagine most would be unaware of the essense transfer until after they’ve already been consumed by it. Then they would look for a new apprentice to continue the cycle.
And I think this fits Palpatine’s character in the previous movies perfectly well, he’s always been presented as the personification of pure evil, he can’t be redeemed or reasoned with, he’s the darkness that must be destroyed. It also explains how he could’ve survived, as his spirit was more than that of one simple man. Makes more sense than him dragging the other spirits from Sith hell for this movie only. It also adds a new layer to Palpatine trying to cheat death, as this is not something original to him, or even Plagueis, but rather something the Sith had been working towards for generations, it makes his manipulation of Anakin even more devious, and it explains why the Sith must be destroyed to bring balance to the Force, as their greed has led to this unnatural ability to carry their essence from host to host, refusing to let go.
I like the prophecy angle for Rey Nobody, I just think you’d have to really get the point across that she could become evil like Anakin, as telling someone that they’re destined to destroy the sith doesn’t really connect to Rey’s inner darkness immediately. I think that could play great off of Rey’s fear of not being able to live up to the legend of the Skywalkers, though. I also really like the originality of the dyad concept, focusing just on that and maybe connecting the dyad to an ancient sith prophecy involving the rule of two would be an interesting inversion of Anakin’s arc, and could explain that Rey’s link to Kylo’s mind allowed her to intrinsically use his knowledge of the force in previous movies.
Yeah, I think if we went with this angle it would have to be mostly through subtext, most of it is already there in the movie, Rey being the sole heir to the Jedi, taking the Skywalker name, destroying the Sith and bringing back balance to the Force, it’s all already there. But for her to have a struggle the focus would have to be on her being the true heir of Vader, basically everything Kylo thought he was meant to be. We already have her struggle with the dark and her visions, Kylo could reveal she’s the one that’s destined to take over the Sith, basically the way the current nobody cut of Ascendant already works, only now we reveal she was destined to take Vader’s place from the start.