Exactly.
I know many people thought Coleman Reese would become Riddler. Riddler wouldve been a good character, especially to test the detective and thinking of Batman. thats something I love, but was only used a few times in TDK.
Nolan needed to do more than just 3 films. The first film was the beginning, the 2nd film was escalation, showing us Batmans increasing detective skills and his belief in good. Psychologically strengthening.
We needed to see batman using his extreme intelligence and detective skills. Doing Riddler akin to Arkham City; Riddler kidnapping people, putting them in contraptions that are like SAW movies.
So that couldve been an option. Hush wouldve been great; Imagine Hush cutting someones face off from the mob, and them turning into Black Mask. A full, Mob warfare in Gotham after Maroni and the crime families fell because of Joker.
Hush and Black Mask, combined with The riddler couldve carried a film, and it wouldve been a very interesting film. Bane with Rhas wouldve been a better alternative. Clayface couldve been a state-of the art convict who can mould faces to himself and become anyone.
I know alot wouldnt like deviating from the comic origins, but the things which couldve been done with more than 3 films, is quite alot. I love the idea of hush making Black Mask and going into a Mob turf war for Gotham. We never got that in BB or TDK. No fight for power when the families fell.
Clayface couldve been very interesting be it making moulding masks or even doing plastic surgery to change himself, keeping inline with the sense of hyper-reality.