Interesting retrospective. Adam posed this in a thread, but I think it belongs as a separate post. The words below are his, not mine.
I saw a documentary today on the 1939 (and 1940) New York’s World Fair. This is the sort of famous documentary narrated by Jason Robards that came out in 1984 called “The World of Tomorrow.” One of the weird things about World’s Fairs, those hosted in the U.S anyway, is that there was often nudity there. I had previously seen a documentary on the 1962 Seattle’s World’s Fair that had nudity. I have no idea how this happened at the time, maybe somebody knows?
Anyway, these are the images from The World of Tomorrow. The first is from an exhibition called Frozen Alive and of the other, Robards narrated “they weren’t science and they weren’t art, they were just there.” They aren’t totally topless though in those.
There was also an exhibit by Salvador Dali with semi nudity, and there was nudity at the related 1939 San Francisco World’s Fair. This is an article on the nudity (and semi nudity) at the 1939 New York’s Worlds Fair.

Famous stripper Sally Rand performed her famous fan dance complete naked in the 1933 Chicago World’s Fair. Aside from Sally, there was also naked shadow dancing at a bunch of scantily clad models. I guess they got away with it because it was art? But I believe Sally was arrested a number of times.
They must have figured that in the future nudity would be no big deal and commonplace. Maybe because the technology to adjust the weather or because we no longer have religion to dictate modesty like that. Kinda like predicting gay marriage or the return of polygamy.
Or maybe they were just using any excuse they could think of to see more nude women.