Despite garnering more than 10,000 supports on LEGO CUUSOO, the Serenity and the overall concept for a LEGO Firefly theme have not passed official LEGO review. The folks over at LEGO felt that the concept for the themes and the sets was not a good fit with their target customer, which LEGO defines as children ages 6-11.
The decision seems a bit hypocritical considering some of the other themes that LEGO has put out ,which could be considered inappropriate for children under 11. For example, The Pirates of the Caribbean, Indiana Jones and Star Wars all feature fairly violent subject matter and are all part of movie franchises which are not targeted at children ages 6 to 11 either. Perhaps it was just a licensing issue where LEGO did not want another Sci-Fi inspired theme to compete with the extremely popular Star Wars lineup.
Unfortunately,this is not the first time LEGO has not approved a LEGO CUUSOO project which reached 10,000 supporters. The Winchester from the movie Shaun of the Dead received a similar thumbs down due its subject matter.