What if they'd handed the #StarWarsExpandedUniverse to @cstross instead of to Kevin J. Anderson, Zahn, et al.?
Obviously there are plenty of dead #Jedi to go around. How many other ghosts are there? Who are they haunting? Obviously even the Sith get to haunt people. Out of the living, can only Jedi see or be haunted by them? Who is the Emperor now haunting? Who haunts Leia?
Are they more easily visible on the jungle and wood worlds? We didn't see them on Hoth.
@cstross might have thought about possession, too.
Perhaps C3PO isn't intelligent, merely possessed by another #Jedi ghost, going incognito and giving the performance of xyr ... afterlife. None of the many other androids on screen behave like that. Did the Cantina bartender actually mean that possessed machines aren't allowed? Has he got The Sight, too?
Are the pieces of the second Death Star, floating around, possessed by the Emperor's ghost?
@cstross doing the #StarWarsExpandedUniverse would say that _obviously_ Luke is a poltergeist in training. Xe moves furniture around with ease.
If only #Jedi can perceive the ghosts, that would explain why possessed C3PO and R2D2 can discuss The Plot openly in corridors/rooms without any of the normals passing by catching on, and why Chewbacca just ignores C3PO's complaining. And, indeed, why Leia, a Jedi, felt that entrusting R2D2 was safe. No non-Jedi could have accessed the message.
JdeBP