Doug, the demand is out there from many Superman fans around the world to see a new SE of "Superman II" with all of the lost Richard Donner footage restored and presented for the first time in an official capacity. The primary indicator of that is the popularity of the Salkind international cut, which remains the one source for much of the Donner footage that was included for television release and is a fan favorite to this day.
Warner Bros. execs have expressed their interest in such a project, and this came from a top-level exec last year. It's now a matter of getting everyone to agree on the project, most importantly Ilya Salkind, Pueblo Film Licensing (who is the current legal receivor of anything Salkind-connected), Mr. Donner, Richard Lester, all of the surviving actors and contributors, the Brando estate, and the Reeve family. Most everyone is willing to participate in the project, and I have it on good word that the Reeve family would most certainly give their blessings to the project. Obviously, it's a race against time before we lose anyone else and before all of the footage is lost forever.
Whether the project results in a new Donner-completed version of II, a cut similar to Kino Video's recent assembled version of "Metropolis" (complete with new music, new intertitle cards and photographs or storyboards replacing scenes that were not filmed or were not located), a cut similar to the Salkind international cut, something similar to the upcoming SE of "Titanic" (with the Donner footage presented in a branching featurette format), or simply a separate section of deleted/alternate scenes, that remains to be decided.
Obviously, the leading decision to have a fully completed all-Donner version of II, much in the aforementioned style of the DVD version of "Star Trek: TMP", is the one most cited by fans. And it could certainly be done, with CGI and new footage completed for the film. This is where brilliant people like Mike Matessino (who oversaw the restoration to the Rhino "Superman" CD release - has it been five years already since it came out?), David C. Fein (who worked with Robert Wise and Mike on the
ST:TMP DVD), and Michael Thau and Jonathan Gaines (who led the work on the "Superman" SE DVD project) come in. However, finding a replacement to complete the necessary scenes Christopher Reeve would have been involved in (I'm thinking the main battle sequence is the one key sequence he would have had to complete - hey DC, clarification, good buddy!) would be necessary and a difficult task - perhaps Brandon Routh would be willing to do some work for it, if Bryan Singer allowed him to.
Don't be quick to dismiss the demand for a new version of II just yet. It's not a lost cause, not in the eyes of many who view it as one step closer to reality.
As for a fully completed SE of "Superman IV", I for one would love to see it occur, but at the same time I'm not holding my breath on the project. Again, it would take time, effort, participation from all parties (most importantly Sidney Furie, Golan and Globus, and the WB), and restorationists to complete and/or clean up the visual FX for the film. It would also take the location and restoration of Alexander Courage's full music score - and there's 105 minutes of music that he did. And it would also require the location of the missing footage. Unfortunately, it's been reported that the 42 minutes of film was destroyed just after the sneak preview screening. Whether the footage was cut and then stored in a film vault, that's not been verified. Again, it would take a lot of demand to the WB to get the project off the ground.
Let's take it one project at a time and see what happens. The success of a new SE of "Superman II" could lead to a new SE of "Superman IV", if properly handled right and if sales on the DVD go really well.