There is an element of some mystery surrounding the fourth "trilogy" that was once attached to the Star Wars. Lucas today denies that he had any plans or story for the third trilogy (Episodes VII-IX), which isn't the case, but we can do one better: what was the story for Episodes X, XI, and XII? Am I crazy? If you've read Secret History of Star Wars you will know what I am referring to--in early 1978, it was announced in Time that there were twelve Star Wars films in the franchise. This isn't a typo; Lucasfilm referenced them frequently in publications such as Bantha Tracks from 1978 to 1980, and Lucas himself even addresses them in the May 1980 issue, stating he had limited the series to nine films instead.
The leaves the issue dangling: what were these films? I have been over some hypotheses in Secret History of Star Wars, and these seem to remain accurate in light of discoveries I have now made. Lucas in 1977 decided that Star Wars would be a franchise, and had it set at unlimited possibilities, like the James Bond series--the films would continue indefinitely, and generally stand alone. Gary Kurtz at the time says the films aren't chronological, and would bound around in time from one film to the next--Lucas himself states that he would like to one day do a film showing the fall of Darth Vader and the murder of Anakin Skywalker.
Lucas had developed some story ideas with Leigh Brackett in November 1977, but based on The Annotated Screenplays this doesn't amount to that much--some info on the Clone Wars is developed, but the only concrete sequel story point is that Luke has a twin sister, as his father's ghost reveals to him, who is also training to be a Jedi across the other side of the galaxy. However, a few months later, in March 1978, Lucas announced to Time magazine that the series would comprise of twelve films, but doesn't offer any specifics. By 1979, in an interview for Alan Arnold's 1980 book, Lucas now has something very different in mind--nine films, comprising three trilogies, chronologically connected, with twenty years in between each set, later elaborating that the third trilogy is about "the re-building of the Republic." He says in Bantha Tracks in May 1980 that the three remainders from the 12-episode plan were "tangential" to the saga, and so axed.
There are some very practical matters here. In Secret History of Star Wars, I maintain that there was little concrete story development done when Lucas had announced the twelve film plan in the new year of 1978--one can see this from the outlook and development of the Empire Strikes Back story conferences of November 1977, where Lucas had few or only vague ideas as to where his story was going. The number twelve, attached to the films just after this, was likely put in place because twelve was the traditional number of episodes in a serial, and so The Adventures of Luke Skywalker, as the series was then called, would run for twelve episodes. I stand by this.
However, I now discover evidence of some of the types of films Lucas was interested in exploring, as he states in 1980. This shows evidence of the undeveloped Bond-like structure from 1977 and 1978. As a precursor, this is what he says in August 1977, in an interview for Rolling Stone:
"I think the sequels will be much, much better. What I want to do is direct the last sequel. I could do the first one and the last one and let everyone else do the ones in between...I would want to try and get some good directors, and see what their interpretation of the theme is. I think it will be interesting, it is like taking a theme in film school, say, okay, everybody do their interpretation of this theme. It's an interesting idea to see how people interpret the genre. Nobody has to worry about what a Wookie is and what it does and how it reacts. Wookies are there, the people are there, the environment is there, the empire is there...I've put up the concrete slab of the walls and now everybody can have fun drawing the pictures and putting on the little gargoyles and doing all the really fun stuff. And it's a competition. I'm hoping if I get friends of mine they will want to do a much better film, like, 'I'll show George that I can do a film twice that good.'...One of the sequels we are thinking of is the young days of Ben Kenobi. It would probably be all different actors."