MiniRock might be the only one to find this interesting, but Liam Neeson claims he recorded the dialogue for the Qui-Gon "ghost" scene for Episode III, at least according to IMDB. It is mentioned briefly about 1/3 down the page.

www.imdb.com/title/tt0121766/trivia

I suppose it's possible George could be saving the scene for future teaser/deleted material in the Star Wars saga release (all 6 movies in one collection) or a future HD release. You know how George loves to dangle a carrot in front of the horse/cart as a marketing tool.....