In an apparent move to generate more hype before the release of Star Wars: Episode VIII, its release date of May 26, 2017 has been pushed back to December 15, 2017. Disney's Chief Star Wars Release Date Officer Bellek Rendix said, "There was 10 years between episodes III and VII allowing massive hype to be generated. There's no way we can come near that amount of hype releasing the movie next May. We think December is the proper time frame."
This also places Episode VIII in contention with Avatar 2, due to release December 25, 2017, a seemingly risky move by Disney, making both sci-fi movies compete with each other. As Avatar 2 has been in production for years, maybe Disney isn't too set on Avatar 2's release date and wants to have a big movie to fill its hole if it gets pushed back.
The move also follows Star Wars: Episode VII's release date being set in December. Previously, Star Wars films were released in May for Memorial Day weekend, but with Rogue One: A Star Wars Story set for release December 16, 2016, it seems a new tradition will be set.
The seven month delay also gives writer/director Rian Johnson more time to allow rewrites focusing more on Rey, Finn, and Poe.