Yes it is true. Things have changed. On set shooting now. #BrimestoneMovie— Martin Koolhoven (@MartinKoolhoven) June 24, 2015
According to Andreas Wiseman from Screen Daily, Rob is no longer attached to Brimstone.
Variety, Deadline and The Hollywood Reporter also have articles about this.
Added Screendaily article with statement from the film producer. Click on the link to read.