No, as far as we know the next film will not be an adaptation of The Dark Knight Returns. But SlashFilm posted a great article featuring an excerpt of a chapter from the book, Tales from Development Hell: The Greatest Movies Never Made? by David Hughes. The excerpt focuses on the history of the Batman film adaptations, including a film which never made it to the screen: Batman Year One starring Clint Eastwood. If you’re a film buff as well as a Batman fan, I’d suggest going here to check it out.