During the Watchmen panel at the SDCC, Zack Snyder expressed his interest in bringing Frank Miller’s The Dark Knight Returns to the screen saying:
There are a lot of other graphic novels out there, but I would love to see Frank Miller’s Dark Knight made into a movie, but that’s just me.
Later at the Entertainment Weekly Visionaries panel, Frank Miller told Snyder:
You can do it anytime you want to Zack
Well while I do think The Dark Knight Returns is a very important Batman story and a very cool read, I do not think Frank or Zack heard of a little film out at moment doing modestly well called THE DARK KNIGHT which in my opinion is the finest Batman story ever! So unless they do an animated Dark Knight Returns it ain't gonna happen.