Maybe I’m missing something, but why is Palpatine lying about being Rey’s grandfather necessary in the first place? It’s not like a massive amount of runtime gets cut if you remove all lines where Palpatine mentions this: depending on how you rewrite the hangar reveal, you can even keep some lines that were originally meant to allude to it. Personally, I think it would be much more effective if whatever reveal Rey gets about her past is actually true, rather than just a blatant lie that Rey can overcome by simply finding out it was a lie in the first place.
It’s not necessary to have the ‘Rey clone’ concept be a lie, but I feel like it would be nice if it remained unconfirmed, especially since there are discrepancies between that story and the ones from prior films. In particular, I think the depiction of the ship Rey sees from her past being different between visions is a hint that her Palpatine lineage is an invention of the Emperor. It just feels like that’s something he would do as a way of controlling someone. It also isn’t really necessary that Rey learns that this story was a lie, just that she comes to realize that the family she may have had in the past isn’t important, it’s the metaphorical family that she has now that really matters.
Jar Jar Bricks’s idea of Rey being a clone is one of the most promising alternate reveals I’ve seen proposed so far (especially given you need to cut practically nothing), but I think one of your earlier ideas, where Rey was trained by Palpatine as a child, still has a lot of potential. It makes both Rey and her parents unambiguous “nobodies” (by blood, at least), while still giving Rey a strong connection to Palpatine. If anything, I actually think Rey having spent a significant portion of her early life with Palpatine is a much stronger reason for her to feel drawn to the throne than “evil genetics” or whatever.
Actually, I proposed both of those ideas. I agree that the first one, where Rey spent time with Palpatine, is compelling in a personal way, and it isn’t even incompatible with the Clone Rey concept. Perhaps this could be the default story, that Rey was a female clone of the Emperor who was being groomed by him as his heir before being kidnapped by Sith cultists and taken to Jakku and Luke’s disciples. This presents the strongest version of the ‘destined for evil’ trope that the saga has ever had, far more than Luke’s evil daddy.
However, this story obliterates the point of Rey nobody; many people thought that Rey coming from nothing was a refreshing concept because they could see Rey’s story in themselves; no virgin birth, no famous or powerful lineage. That was the one redeeming characteristic of the character to many people, my girlfriend included. So when TROS revealed that she was just one more nepo baby in this ever more tiny and incestuous universe, it killed any remaining interest for a lot of people. That, above all else, is why I think it’s important that we not kill the idea that Rey could genuinely come from nowhere, and that’s why I’m fighting so hard for a way to keep the Rey clone story as just a story, however cool it is. The point of the film, after all, is that Rey is able to choose the version of her past that she wants, or reject them all…and she does, choosing an ennobling fiction over the prospect of a humble past or an evil one.