They have tried this a number of times. With the exception of the last couple of batman movies, DC characters don't make money at the box office. I know they are trying again with superman this summer. I'm guessing that whatever happens monetarily with that, will determine how the studios will proceed with other DC characters. The movie they are working on is currently set to be out in 2015, but like I said, if the other movies don't make money, don't expect to see it released.