An idea was discussed recently, possibly on a different thread, was Palpatine being stripped of his physical form and becoming more of a primal negative energy. While that’s maybe a little far, I think it could be neat having him as a sort of spirit (no, not a Sith ghost, Sith can’t do that) who needs a host to inhabit and tries to get Rey to act as that host. Remove shots of GLaDOS Palps and rearrange his lines about his spirit passing into her and it should be doable. Then of course he absorbs the energy of the dyad and emerges as a physical being once more.