My question is this: At what point do they merge, thus creating a virtual reality experience for the user(s)/movieoer(s)?

Instead of going to a movie, you and your pals go into a movie?

Maybe there'll be the movie equivalent of karoake, where you perform a role in a hologram of a scene from a favourite movie while your friends watch and applaud.

Sound freaky?  I don't think so.

Modern gaming does make you an actor of sorts, but you're external to the action, not a part of it.

I suspect that within my lifetime, that will change.