I was watching the end of Raiders of the Lost Ark this evening and it occurred to me that all the supernatural parts of the film begin within the last 20 minutes of the film. Up until that point there were no ghosts. The same with both The Last Crusade and KOTCS. It's instructive in that KK was the Executive producer on those films, all of which were Lucas projects. It could be the way the entire ST ends. In fact it would be best if the plot consisted of no Force Ghosts at all until the end. Luke dies but doesn't disappear. The Force is waning. Life is in the balance. The protagonists are on their own... Luke is dead and unable to crossover and the new heroes have no ability to contact or commune with their Force Elders and Descendants. Also, the Holograms of the Jedi in the PT look like Force Ghosts, especially during the council meetings...foreshadows? Take a look if you want to get used to the idea.