Batman-News.com had the details on an interview that David S. Goyer did with Empire magazine about the details.
At the premiere for The Dark Knight in 2008 he says the studio already had their mind made up. They said, “it’s gonna be The Riddler, and we want it to be Leonardo DiCaprio…”
The same interview confirms that Nolan and Goyer didn’t even know how the movie would go or who the villain would be until the fall of that year, but they did know how the film would end and Goyer says it hasn’t changed from their original conception. “When Goyer saw that final scene from The Dark Knight Rises, he got a lump in his throat.”
The Dark Knight Rises hits theaters July 20.
