I think this is one area where Lucas is the most misunderstood. I don't think he denies ever talking about doing 9 films, just that he only ever got around to fleshing out 6.

From what I understand any of the things he had been talking about with regards to doing a third trilogy had to do with a newly teamed up Luke and Anakin overthrowing the Emperor. As you can see, Lucas just condensed the "third trilogy" into a 5 minute change of heart sequence in ROTJ.

So even if he was thinking about making it 9 films, the story is pretty much over in ROTJ.