Tomorrowland 2055 was to be an updated version of Tomorrowland..... One of the main attractions that was to be added was Alien Encounter. Initially Disney owned the right to the alien from the movie Alien and planned to use that as the alien, but some Imagineers thought that it would be too scary. There was debate over it and the Imagineers got George Lucas to convince Michael Eisner that it was too scary for Disney.
- Chris Ware, Disney Unbuilt: A Pocket Guide to the Disney Imagineering Graveyard (2016)
The book itself is not particularly well-written (I think, despite the Amazon/GR tagging, this is not Jimmy Corrigan-Chris-Ware), but there are a lot of interesting fun facts in here. As well as the Alien inclusion in Tomorrowland, there were also plans for a separate Nostromo ride. Other fun facts include the Black Cauldron and TRON attractions that never happened (but design fragments from the former wound up in, of all things, a Cinderella ride), as well as MYST Island, because, ... MYST.
Other, slightly creepier, ideas include the various country pavilions (all with planned corporate sponsorship!), with the Soviet Union Pavilion a baffling highlight, and about 10,000 different creative re-imaginings of 'American Mythology', including a Civil War themed attraction that is about sixteen types of terrible idea. Walt Disney's original scheme for Epcot - a Utopian micro-city - is also included, and would make an excellent backdrop for fiction.