The trilogy is the classic model for releasing science fiction, fantasy and comic adaptations. Successful trilogies include Star Wars, Lord of the Rings, Back to the Future, The Matrix, Twilight, The Hunger Games and many more.
But in today's media environment, a predefined trilogy leaves money on the table when a fan base will support more than just three movies or books.
A creator can start with a larger pre-planned arch. JK Rowling planned 7 books for the Harry Potter series, which somehow became 8 movies. But that still leaves a preset end to the series that is very difficult to expand beyond.
Recently, the plan seems to be what I'm calling the "cycle." A series of movies featuring individual characters, culminating in an ensemble movie. Then the cycle starts again.
Look at the current set up of the Avengers films:
The same structure appears to be at work with DC Comic's rumored Justice League series. And now as part of the Disney Star Wars acquisition, there will be stand-alone movies featuring individual characters along with the new trilogy.
From a business standpoint, it makes sense. The cycle can continue as long as there are enough fans to support it. Movies can come out more frequently to keep fans connected to the series. And with no predefined end to the series, the studios can maximize their profits.
Creatively, writers can do more character development in the individual movies. Which in turn makes the ensemble movies that much more powerful. With The Avengers cycle, Joss Whedon serves as a creative consultant for all the films maintaining a degree of continuity.
I'd expect to see other franchises try to adopt this format. And it will be interesting to see how successful the Marvel, DC and Star Wars cycles will be in the long term.