XSI Base has posted an interview with Concept Illustrator Ben Procter who talks about a cut sequence from Superman Returns which may be used in the sequel:

Tell us about your involvement in Superman Returns and what illustrations you had to create

Sadly, much of my work on Superman Returns never ended up in the final film, because at the last minute a big introductory sequence where Superman returns to the shattered remains of Krypton was dropped to help keep down the running time. But at any rate, I worked on a variety of elements for this lost sequence, including the destroyed planet itself and both the exterior and interior of a large crystalline ship which has carried Supes from earth. The interior was fully built and photographed as a translucent, glowing set which I've only seen in one photograph in the Art of Superman Returns book. Bryan Singer's group has made noises about including the lost sequence in a sequel film, and I sure hope they do that so I can see how it turned out! Also cut from the release was a scene where teenage Clark Kent discovers the hidden remnants of the Kryptonian space pod which brought him to earth as an infant. I modelled the pod in 3D, once again working within a crystalline, alien style of construction.

Happily, my work on the Fortress of Solitude made it into the movie, at least in some form. I did a full interior model which became the basis for a partial set construction, and was also used by Collin Grant in storyboarding the FOS sequence and by Jeff Julian in his concept illustration of the Jor-El ice crystal holograms. In developing the FOS interior model, I took a good look at the set from the Donner Superman films, as production designer Guy Dyas wanted everything for the movie to harken back to the earlier designs in some ways while at the same time taking them to a new level. Taking a ton of screengrabs from the Donner films and roto-mapping them into roughly matched 3D camera views, I was able to more or less reconstruct the basic layout of the old FOS set, and from there we added greater scale, a more intricate composition of angular elements, more crystalline growth detail, and a big vertical construction/launch chute for Superman's crystal ship.

I also modelled a FOS exterior entrance staircase, based heavily on Tani Kunitake's storyboards, which became an important part of the exterior set for Luthor's island grown from the seafloor.

Superman: The Man of Steel, the sequel to Superman Returns is scheduled to arrive in theatres in 2010.