In a recent appearance on Charlie Rose, John Lasseter revealed the rough premise of an upcoming-but-untitled Pixar film:
Pete Docter, from Monsters, Inc. and Up, is doing a new film that takes place inside of a girl's mind and it is about her emotions as characters, and that is unlike anything you've ever seen.
With Brave and now this, it looks like Pixar is finally taking their lack of female lead characters seriously.