I keep seeing conflicting things on that... Wookieepedia has him basically stating no, and he never wrote anything for it, it's about Vader, etc... Like the Prequals (and the confusion surrounding how much of those he says he knew at the time the OT was made compared to what he says now), this is murky and his story sort of changes... Here's a couple quotes:
Interviewer: "Do you think you'd have other people continue the Star Wars saga past Episode VI or turn some of the other material into films?"
Lucas: "But there's no story past Episode VI, there's just no story. It's a certain story about Anakin Skywalker and once Anakin Skywalker dies, that's kind of the end of the story. There is no story about Luke Skywalker, I mean apart from the books. But there's three worlds: There's my world that I made up, there's the licensing world that's the books, the comics, all that kind of stuff, the games, which is their world, and then there's the fans' world, which is also very rich in imagination, but they don't always mesh. All I'm in charge of is my world. I can't be in charge of those other people's world, because I can't keep up with it."
TOTAL FILM: "The Star Wars universe has expanded far beyond the movies. How much leeway do the game makers and novel writers have?"
LUCAS: "They have their own kind of world. There's three pillars of Star Wars. I'll probably get in trouble for this but it's OK! There's three pillars: the father, the son and the holy ghost. I'm the father, Howard Roffman [president of Lucas Licensing] is the son and the holy ghost is the fans, this kind of ethereal world of people coming up with all kinds of different ideas and histories. Now these three different pillars don't always match, but the movies and TV shows are all under my control and they are consistent within themselves. Howard tries to be consistent but sometimes he goes off on tangents and it's hard to hold him back. He once said to me that there are two Star Trek universes: there's the TV show and then there's all the spin-offs. He said that these were completely different and didn't have anything to do with each other. So I said, "OK, go ahead." In the early days I told them that they couldn't do anything about how Darth Vader was born, for obvious reasons, but otherwise I pretty much let them do whatever they wanted. They created this whole amazing universe that goes on for millions of years!"
TOTAL FILM: "Are you happy for new Star Wars tales to be told after you're gone?"
LUCAS: "I've left pretty explicit instructions for there not to be any more features. There will definitely be no Episodes VII-IX. That's because there isn't any story. I mean, I never thought of anything. And now there have been novels about the events after Episode VI, which isn't at all what I would have done with it. The Star Wars story is really the tragedy of Darth Vader. That is the story. Once Vader dies, he doesn't come back to life, the Emperor doesn't get cloned and Luke doesn't get married..."
I'll say this... I like Leeland Chee because he's an interactive guy with the fans, and passionate, but Lucas as a boss made his job nigh on impossible. Howard Roffman as well, though he was seemingly less involved in a direct way with the fans.
Now, for me, this was never that big an issue. But for LFL, it was... It was like they HAD to try to keep things cohesive and retcon everything for the fans, or select groups would go batshit over something.
I admit too, I dislike when they step over existing EU tidbits, but mine usually aren't plotpoints. They're things like, "Why did ROTS use AT-RT's, which were **** from a military perspective, when the AT-PT was established in EU even as a vehicle from the Clone Wars era, and was miles superior?"
Well the reason there is because the AT-PT's less visually interesting obviously, but it made more sense. Damn my logic. But yeah that's kinda the stuff I sit and bum about wishing we'd seen... Maybe we will in Rebels? I can dream.
BUT, Lucas says in the last quote above that he doesn't even more features, much less 7-9! He directly addresses he has no story for 7-9 either, and that he'd never have made it anything like any of the EU he'd apparently heard about but never read (according to himself).
Is he lying? Maybe, I dunno. I don't think 1-3 were fleshed in 83 like he claims they were, frankly. I think he maybe had a ballpark idea, but not what we ultimately see. Maybe he had a ballpark idea on 7-9, but he's pretty vehement there that this is Vader's story, not Vader's kid's story.
If Lucas is the all-powerful and people are rigid about that stuff too, it's funny that that quote basically wipes out Mara Jade all together too. Good times.
Canon is a word someone is trying to force on you... Be yourself and enjoy Star Wars however you want. You'll feel better. Acknowledge only the movies. Or only the original movies. Or only the PT. Or everything. Or just one movie. Whatever.
In my dipshitty Star Wars world, the Empire has the "Aliens" from the Alien films captive and are experimenting. Kyle Katarn was sent to their base where the presumed biological warfare experiment was taking place to get information on it. Xenomorphs escape. Fun ensues. The Empire poops itself to clean up the "spill", and Katarn hauls ass from the planet (a desolate rock of a moon) not really knowing what he saw, just knowing he wished he hadn't!
Why do I crowbar that into my SW universe? Because it fits because I want it to, and I dig Kyle Katarn, and once I played a custom level to Jedi Knight that was exactly that storyline, and it was one of the greatest Star Wars games I ever played in my life, made by a fan who didn't care if you told him, "but it's not canon!", since he did it just for fun and to make people smile.