The previous 'dead Jedi' ghosts have only come back as spiritual guides, right? So The Emperor should only be able to do likewise? I really struggled with seeing Maul at the end of the otherwise great SOLO. As a SW fan who has pretty much enjoyed the new films*, apart from ROGUE ONE, I worry Abrams, in trying to pull the/some fans back, might deliver some kind of 'magic blood' buffoonery I'll struggle to sanction. I have a bad feeling about this. Colour me troubled.
*yes, even THE LAST JEDI, which I thought was mainly enjoyable, despite some mis-steps and such (Leia Poppins/the whole Canto Bight sequence/Luke's motivations/acts).