It’s not unusual for a film this early in its pre-production to get some additional help. For the 2019 release of Star Wars: Episode 9, the film’s script is getting a rewrite. The first draft of the film was co-written by the film’s director Colin Trevorrow and Derek Connolly. Lucasfilm seems to have been happy with the progress made so far ahead of the May 2019 release. But with Trevorrow hoping to start filming in January 2018, it gives them around five months to get all the pre-prod stuff done. Apparently, one of the things they want to do is give the script a once-over. Screenwriter Jack Thorne is supposedly coming on board to work on the script. He’s worked on things like Skins, National Treasure, and BBC’s His Dark Materials adaptation, among others.
It isn’t known how much Thorne has to do on the screenplay but with production schedule seemingly still the same, it might just mean that Thorne is coming on as a script doctor and reading over what’s been done and making edits where needed.
Source: Screen Rant