Also revealed in this interview is that Bryan Singer has indeed been signed to do the sequel. This from IESB.net
You saw "The Dark Knight?" Did you enjoy it?
Brandon Routh: I did, I did, on many levels, it was really amazing. I thought the movie as a whole was a great ride and I watched the behind the scenes of the first one about the fighting style, so I was really paying attention when I watched this one, I wanted to see more fighting because I really saw how strong and powerful the moves are. It was pretty impressive.
A lot of people don't think Superman can be that dark, or that you could make such a dark Superman film.
BR: I don't know, I don't think the character necessarily has to be darker, I think he is kind of dark in a sense, emotional dark, in Superman Returns, and the movie as a whole was slightly dark, they could have had more prowess in it I suppose, and I think that's one thing that can be done in the sequel, so I don't know how much darker you want to make it necessarily. You make the stakes higher, you make the villain darker, I think that's a way to do it. But I don't think Superman himself needs to be darker. He definitely has to struggle, how does Superman be a part of the world? And does he have to make sacrifices to be a part of that world? To fit in and what purpose does he really play in the world? Those are all kind of dark places to explore. But, I don't think Superman should ever be dark and brooding, that's not is nature. And that's now what people what to see. Like Brainiac or something like that, a situation when the villain is...
Would that be a good, if you had a choice is that the villain you'd like to see in the next Superman?
BR: I think it would certainly be interesting, I think there are a lot of things you could do with Brainiac. He's been given a lot of power and a lot of different abilities over the years in the comics, as far as I understand. I know that DC is working on a Brainiac storyline that they are excited about and I think combining the two and have that flow between the comics and the movie would be a nice thing. I honestly think there are a lot of interesting things you can do with Brainiac. Controlling people, controlling technology, a lot of cool things.