The rumor is that WB wants to reboot after this one.
I hate this trend lately with comic movies; they make 3-4 of them and then reboot. Marvel started it and I hate them for it. They need to do what you suggest, leave it open and then let another director take the helm in a few years. Batman can continue. They have so many more villains to go through in this series.
I agree about the Superman movie, I think it's going to be good.
