Disney's America was supposed to have a film or presentation that celebrated immigration that would have been housed in a recreation of Ellis Island. That morphed into Golden Dreams and the Palace of Fine Arts in DCA.
DA was going to have a farm area, just like the Bountiful Valley Farm at DCA. It was also going to have a section with factories or workplaces. The above mentioned roller coaster was going to be part of that - it was a roller coaster through a steel mill.
It was also going to have an amusement pier. Disney also had an amusement pier planned for the Port Disney project in Long Beach.
DA also had Liberty Field, a recreation of an old airfield that I think was going to be themed to WW2, but it's the ancestor of Condor Flats. And there was going to be a Lewis & Clark expedition raft ride, similar to Grizzly Peak.
DCA is pretty much DA, with the addition of the Hollywood Pictures Backlot.