Mitchell and O'Brien worked on the stage mounting of the musical Hairspray, with Mitchell choreographing and O'Brien directing. They were both expected to make their feature film directorial debuts on the Hairspray movie.
The reason for the team's exit was reportedly a change in the production schedule. The film, once scheduled for a fall start, is now slated to begin shooting in the spring. The move caused a conflict with O'Brien's theatrical endeavors and therefore both Mitchell and O'Brien departed.
Rob Marshall is the top choice to replace Mitchell and O'Brien on the film. Not only did Marshall direct the mega-hit film adaptation of Chicago, but he was the original director/choreographer of the stage Hairspray. He left Hairspray to film Chicago during the development stage.
There is no word yet on whether the director switch will affect casting. Variety previously reported Billy Crystal and Aretha Franklin were in talks to play Wilbur Turnblad and Motormouth Maybelle and John Travolta was the frontrunner for the drag role of Edna Turnblad.