Fans will probably have to wait more than 6 years for another Superman movie if this bombs.
There's so much pressure for "Man of Steel" to work. It's the second attempt revive the Superman franchise since "Superman Returns"
With Green Lanterns failure, "Man of Steel" has to lead the charge for future DC movies to be greenlit.
If "Man of Steel" fails expect the Batman reboot(with Nolan producing?) to be greenlit in a second.
It will be more Batman movie for the foreseeable future for DC