Regarding Snoke/Palpatine, we actually get Palpatine’s motif when Snoke is torturing Rey in TLJ. While Williams probably just threw it in there, it at least makes it somewhat of a hint in retrospect. Perhaps Palpatine’s motif could appear in TFA as well in one of Snoke’s scenes.
I was going to add it to his last transmission with Hux, since i changed the line to “Leave the base at once and have Kylo Ren come to me. It is time.” I use this to set up Kylo travelling to Exegol, and using the Emperor’s theme would really help cement that.