To answer the question, yes I believe he will. Why? Now there is another can of worms. I have always thought of the ghosts appearance to coincide with the Jedi's connection to the living force. Qui-Gon was very much into the whole will of the force thing as if he was being controlled by it perhaps to some greater degree than others. His midichlorian explanation to anakin tells us of these microscopic beings as the reason the powers jedi have exist. His coming back to explain the connection between the force and living or dead beings will happen I am sure in ep. III. He will explain that to be one with the force and to be able to control the midichlorians in you is how you will be able to carry your life force through death and beyond. Your connection to the force and force users will enable you to appear to them as an apparition caused by these microscopic beings (midichlorians). I know it may sound strange and it just may suck, but I think this is where GL is going with this. The midis form a ghost like formation allowing you to retain your identity in the afterlife. Yoda gives evidence of this in ESB "luminous beings are we not this crude matter" its all right there. Yoda learns this from somewhere most likely qui gon or obi "it surrounds us binds us together" Wan Kenobi. So at one point qui talked to one of those two his connection is with obi, yodi, and ani so his absence in 4,5,6 is plausible Perhaps he still talks to anakin we don't know. He has no connection to luke so he does not appear to him in ROTJ Nor does he shape or mold him that is Obi wans job. Random ghosts popping up out of the blue talking about destiny and such would scare the poor little farm boy I would imagine so he lets the living handle that. So is qui the one who discovers this ability? Yes, I think so. He discovers it post mordem which is why he does not dissapear. Obi and Yoda and possibly Anakin knew it before they die so they dissapear because of it. The problem becomes ROTJ. How is it anakin learns of this between 4 and 6? We may never find out. But heck while I am at it why not throw this out there perhaps anakin does know of it but vader does not. Now there is another thread altogether. Am I completely wrong in this theory of mine? Probably but it sure is fun to speculate. The answer is probably much easier than that.