I think the Rey killing her parents angle is good if you wanted to cut less in general, but I wonder if you could make the reveal focused on a vision of the future, rather than a glimpse of the past.
Maybe Rey and Kylo have a shared vision early on that is just in fragments. Kylo starts goading her into seeing the rest of the vision, and the big hangar reveal is Kylo outright stating what the vision was.
The Resistance will fail, and Rey joins Palpatine. Maybe they even see Rey will be the one to kill her friends (with Force lightning). That probably would be “shocking” to her. But Kylo Ren presents her an alternative: join me and we can keep that from happening. We can save your friends.
I think this would also work well as motivation for Rey to want to kill Palpatine, a reason for her to possibly join Kylo, and a reason why she sees self-exile as a better alternative than facing Palpatine. Plus, it keeps Rey’s focus on her newfound family, which is at the heart of the story, rather than digging up her past again.
Don’t get me wrong, I like the Rey killing her parents angle too. It actually makes me think of the DotF script, which had Kylo be the one to kill her parents, but I could totally imagine how easy that change could’ve been made to have Rey be the one to do it.
Even with the killing parents change we’d still have to cut a lot of the parent stuff out. This idea would just go slightly further and not dwell on Rey’s past at all. I think the idea of Rey being haunted by her potential futures ties in well with Rey trying to forge her own identity after the reveal in TLJ. Because, if you think about it, if Rey killed her parents, Kylo should’ve really revealed it in TLJ. God, imagine Rey’s reaction then. She probably would’ve joined him. So another parental reveal just feels sort of redundant. At this point I think it could be better to focus on her future, rather than her past.