Originally, that would have taken place in Episode 9, but he ended up pushing that resolution up to episode 6.
Hence he never came up with sequels to follow ROTJ.
Notice when you put that quote you just took back into context, he is actually acknowledging that his plan did change.
The long-standing perception has been that the complete Star Wars saga is a 9 film cycle, and after Episodes I through III were finished Lucas would move on to Episodes VII, VIII, and IX, resuming where Return of the Jedi had left off. "That's really not part of the plan AT THIS POINT, " he says. "When you see it six parts, you'll understand. It really ends at part six."
Whereas the prequel plotlines have their basis in the original treatment for Star Wars that Lucas wrote in the early 1970's, "I never had a story for the sequels, for the later ones," he says.
Whereas the prequel plotlines have their basis in the original treatment for Star Wars that Lucas wrote in the early 1970's, "I never had a story for the sequels, for the later ones," he says.