8 documentaries about notable movies that never happened

Movie fans often like to speculate about films that never got made.
For instance, what if Steven Spielberg had made “American Sniper” instead of Clint Eastwood? Spielberg was originally slated to direct the biopic and planned to take the movie in a different direction.
Last year I noticed the emergence of a subcategory of documentaries about interesting movies that were planned but never completed. In some cases, these movies were ultimately shot by other filmmakers who put their own spin on the material. Some never made it past pre-production.
What follows is a list of documentaries in the subgenre about movies that could have been. Some of these documentaries are still in production or pending release.

Jodorowsky’s Dune

“Jodorowsky’s Dune” (2014) explores Chilean-French director Alejandro Jodorowsky’s unsuccessful attempt to adapt and film the classic science-fiction novel “Dune” in the mid-1970s. Director David Lynch helmed a much derided 1984 film version of the novel. (See articles by Wikipedia, Entertainment Weekly and the Verge.)

Lost Soul

“Lost Soul: The Doomed Journey of Richard Stanley’s Island of Dr. Moreau” (2014) recounts the making of the 1996 box-office bomb “The Island of Dr. Moreau.” The original director of the film, Richard Stanley, was fired after just a few days of principal photography and replaced by veteran journeyman director John Frankenheimer. (See articles from Entertainment Weekly and Wikipedia.)

Doomed! The Untold Story of Roger Corman’s The Fantastic Four

“Doomed! The Untold Story of Roger Corman’s The Fantastic Four” tells the story of the ill-fated movie version of the Fantastic Four that was executive produced by low-budget filmmaker Roger Corman.
The documentary is expected to be released this year. (See articles by Indiewire and Comic Book Resources.)

The Death of Superman Lives: What Happened?

“The Death of Superman Lives: What Happened?” is a documentary about the proposed 1998 “Superman Lives” feature film that would have starred Nicolas Cage and was to be directed by Tim Burton. It is set for release this year. (See articles by IMDb, Geek Tyrant and another by GeekTyrant.)

A World War II Fairytale: The Making of Michael Mann’s The Keep

“A World War II Fairytale: The Making of Michael Mann’s The Keep” is a documentary in the works about the making of the 1983 cult horror movie “The Keep.” Mann’s film was cut by the studio from its original runtime of over three hours to just over one-and-a-half hours. (See article by Shock Till You Drop.)

Those are some recent examples of the documentary subgenre. But there have been others before them.

Lost in La Mancha

“Lost in La Mancha” (2002) is a documentary about director Terry Gilliam’s doomed attempt to film, “The Man Who Killed Don Quixote,” starring Johnny Depp. (See article on Wikipedia.)

Marilyn Monroe: The Final Days

“Marilyn Monroe: The Final Days” (2001) documents actress Marilyn Monroe’s unfinished final film, the romantic comedy “Something’s Got to Give.” The documentary includes a 37-minute reconstruction of scenes from movie, which was canceled after Monroe’s death. (See article on IMDb.)

The Epic That Never Was

“The Epic That Never Was” (1965) is a documentary that tells the story of the aborted 1937 filming of “I, Claudius,” starring Charles Laughton, with all of its surviving footage. (See articles on IMDb and the New York Times.)

Let me know if I missed any other good examples.

Update (July 16, 2015): Check out more documentaries about movies that were never made.