What was in the location of the Fantasyland Theatre before it opened as Videopolis in 1985? Was it just backstage?
It was nothing. When the berm was pushed out for Small World it created an empty space that just became known as "the meadow." I don't think that was an official name for it, and most likely just came from the train narration that referred to it as such. During the period between 1966 and 1985 there was no fantasyland station - so the train just kept on going!
You can see the meadow here in this aerial from around 1977:
And here is a video highlighting the construction (Skip to 3:00 for Videopolis):
^ OMG... The Hoff, Julian Lennon, Donna Summer, The Pointer Sisters, Roy Clark.... and then Julie Andrews goes and goofs by saying "Happy Birthday, Mickey!" instead of "Happy Birthday, Disneyland!" But... Emmanuel Lewis did the same thing on WDW's 15th Anniversary special.
and then Julie Andrews goes and goofs by saying "Happy Birthday, Mickey!" instead of "Happy Birthday, Disneyland!"
I don't think that's a goof. It was pre-taped, so if it was a goof, they would have fixed it.
Mickey Mouse is so completely tied to Disneyland, that it seems natural to with Mickey a Happy Birthday, even though it wasn't his specifically. Had Walt still been around, it would have been just as natural for her to say "Happy Birthday, Walt".