I’m still hoping that Sheev isn’t overused in TRoS and remains as just a Force ghost or holocron. This whole Sith trooper thing is concerning. Hopefully they’re just a First Order/Knights of Ren faction.
My worst case scenario for 9 is that it’s revealed that everything leading up to it was some master plan by Palpatine to create a new Sith Empire or something. Evil Sith master plans have been used too much. I want to see Kylo as a conflicted villain that’s struggling to hold the First Order together.