A report from all the way back in 2014 before The Force Awakens was released. There were reports that JJ Abrams was interested in Vader returning as some kind of villain, many rightfully wondered how this was possible when the concept art for TFA was released, we saw a clue, in the drawings of a “Sith Wraith” a type of Sith Ghost that was part Anakin and part Vader. This shows that JJ and company already were thinking about evil force ghosts back before TFA went into production.
Lastly in the trailers we have seen various shots of Rey in the Emperor’s throne room, what is interesting is that she is seen looking up with a seriously freaked out look on her face. We can also see how the throne room looks abandoned and unlived in, why would Sidious if he was alive live somewhere so decrepit? Especially when we have seen his penchant for comfort and luxury before. Sidious as a Sith Ghost would explain this.
We know Sidious will return as a villain, and we know the film is also looking to bring a definite conclusion to the Jedi/Sith conflict. What if Darth Sidious is the all-powerful Sith that’s controlling whatever the dark side is? It could be that Episode IX will by finally destroying Sidious once and for all be destroying the Dark Side once and for all, as well!
If this is true, we could be seeing some epic action scenes taking place in the netherworld of the force, and this could include Jedi like Luke, Obi-Wan, Yoda, Qui-Gon Jinn and Anakin facing the Dark Lord of the Sith.