There have been rumors of other directors being offered the PT. I've heard Spielberg, Darabont, and other names mentioned before, but there's only one name that I know of that's actually stated that he was approached to do it. In his introduction to the book "The Cinema of George Lucas," Ron Howard revealed that Lucas approached him, but Howard wanted Lucas to get back to directing, so he declined and encouraged Lucas to direct it instead. Lucas has said that he originally intended to only direct Episode I and hire other directors to do the other two.