I very much doubt this film will bomb. It may or may not be as good as the anticipation, but this series had a huge number of followers who miss the show and will go to see the film regardless. The film is only just beginning to get test reviews because I'm guessing the studio don't want too much about the film itself leaked too early.
As for the Cynthia Nixon interview, it's all obviously part of the beginning of the publicity to hype up the film. As for the spoiler - it could be anyone of the minor characters, but I doubt it would be one of the main four.