I had an idea for a Metropolis part 3 album a while ago. It's a very vague idea because I don't have an imagination to flesh it out to a song-by-song basis, and I'm not sure it would work even if I did, but I thought it was somewhat interesting. So I may aswell go ahead and share it.
Basically, the album wouldn't continue on from part 2 but instead jump back to the early 1930's. The album would follow the efforts of the private eye hired to investigate the murder/suicide of Julian and Victoria. The album would have a very "hard-boiled" detective theme like the comic books from around that time, or films made later, like The Maltese Falcon. For anyone familiar with Bogart's films, the PI would be a very similar character to what he played in a lot of films, but especially The Maltese Falcon. Now before anyone asks, no, the PI is not Julian, and at this point Edward is still alive, so the PI is a completely new character to the story. The PI would have been hired by a mysterious, beautiful young woman (or "dame") who believes that the events of Julian and Victoria's deaths are not understood, and she convinces him to investigate the circumstances of their deaths. Of course, this dame would be an apparition of Victoria - not a reincarnation, since there wasn't enough time for her to be "reborn" yet, as it were, and her mysterious nature would be another ongoing theme for the PI throughout the album, until he eventually figures out she's an apparition. Of course Edward ends up being one of the first people he talks to about it given his relationship with the deceased, and the PI's dealings with him are how he gets the idea he is involved and Edward's plot to thwart his efforts is another ongoing theme throughout the album. Anyway eventually the PI figures out Victoria has come back to try and help him solve the murders, and he figures out that it was Edward, but of course Edward murders the PI before he can do anything about it.