Question about Harvey Dent in the Dark Knight film?

I was under the impression that, in The Dark Knight, Harvey Dent wouldn't become Two-Face (it seemed like that would happen in the third). Now, Eckhart and Nolan are both saying that Two-Face will make an appearance. I'm concerned that this film will end up being overstuffed like Spider-Man 3, focusing on the important storylines of three different characters.