https://www.youtube.com/watch?v=owrmLeX20CY
That some one incorporates this into either ROS or the other 2 sequels as a nice tie for Darth Vader/Anakin (Could just be in his head as there is a great clip of Ghost Anakin with Yoda and Obiwan helping Rey against the Emperor). Also helps add the Emperor feel, by way of vader. Maybe its one of Palpatines professed voices/visions he gave Ben.
Edit- Could do it in Force Awakens since they’re already on that planet, or intro to ROS when Ben is searching for wave finder, before going to Mustafar
I used this in TFA. It’s awesome!!