After the original announcement on 12th March 2015 that Star Wars: Episode VIII (by Rian Johnson) would open 26th May 2017 (fourty years after the original Star Wars by George Lucas), Disney have since pushed it back to 15th December 2015. The initial reason speculated was that Star Wars: Episode VII – The Force Awakens (by J. J. Abrams, Lawrence Kasdan and Michael Arndt) grossed the highest opening weekend from the 18th – 20th December, something Disney wanted to repeat with Star Wars: Episode VIII. But now, a BBC News article has mentioned that
there had been speculation that the script was being rewritten
While it doesn’t mention any specific sources that have speculated this, it does go on to mention that
Disney did not say why the film had been delayed
implying that there was a less optimistic reason for the rescheduling. The next Star Wars film to be released will be Rogue One: a Star Wars Story (by Chris Weitz and Gary Whitta) on 16th December 2016. Star Wars: Episode VIII‘s rescheduling from 26th May 2017 has now widened the release gap to twelve months, rather than the previous six months. Rogue One: a Star Wars Story itself releases twelve months after Star Wars: Episode VII – The Force Awakens, the shortest gap between two Star Wars films releasing. Star Wars: Episode VIII opening six months later was to shorten that gap further still.
That said, each of the three films from the new Disney regime still open exactly a day before the previous film in the following year. But, 2016 being a leap year means that the gap between Star Wars: Episode VII – The Force Awakens and Rogue One: a Star Wars Story is still 365 days, making the gap between Rogue One: a Star Wars Story and Star Wars: Episode VIII just 364 days, which remains a record.