In the interview that is recorded in Bakemonogatari's official guide book......
Nisio Isin: I have a question that I want to ask as well. In the future, what sort of characters does Hanazawa-san wish to tackle?
Hanazawa: I wish to take on the role of those characters with a very bad personality. As I had not acted for a really evil character before, I wish to challenge that at least once.
Nisio Isin: I understand. Then in the future, the <Bakemonogatari> series will have an evil girl added to it, so please be her voice actress as well. Or, I can write Nadeko as an evil girl - such a plot isn't too bad either.
Hanazawa: Which means to say that she will become 'Dark Nadeko'. *laughs* Please do that.