I agree that Gordon-Levitt deserves the chance especially after the build-up at the conclusion of TDKR. Anyone who cares about comic book films will have seen that movie already so minimal exposition is required.
People are still confused by this. MoS is set in a different continuity than the Dark Knight trilogy. There is no JGL/John Blake/Batman in the MoS universe. There is only Bruce Wayne. The DK trilogy never happened. Granted, the new MoS Batman will be very, very, VERY similar to Bale's Batman because that's where the money is. But they won't be identical.