A lot of people have asked about who actually wrote on Rogue One: A Star Wars Story. The answer is a team did and not a person. From what I have heard over the last year, there were a total of four writers. Gary Whitta wrote the first draft as is publicly known from the initial press release. The writers that followed Whitta’s initial work were Chris Weitz, Scott Z. Burns, and Christopher McQuarrie.
Scott Z. Burns is a name I don’t think has been publicly associated with Rogue One yet. From the sound of things he had a pass at the script after Chris Weitz in 2015. It sounds like Christopher McQuarrie did the rest of the passes after that. The true succession of writers is still obscured and we are not sure if they worked together or in what way.
Interestingly, PU-239 is about:
A worker at a Russian nuclear facility gets exposed to a lethal dose of radiation. In order to provide for his family, he steals some plutonium and sets out to sell it on Moscow’s black market with the help of an incompetent criminal.
This sounds sort of similar to certain plot threads in Rogue One.
It is pretty common for larger films to have several writers onboard and it isn’t a doom and gloom situation on that front. It just took some time to get the script as good as it could be.