Do you expect all the physical evidence of Elephants, such as bones, tusks, genetic samples, stuffed animals, photos and peer reviewed zoological descriptions, to disappear in the next 200 years? If so why? The Dodo went extinct 340 years ago and nobody thinks they were mythical. The mammoth even before that. Even dinosaurs are known to have existed, as a fact. We have vast amounts of physical evidence. So I really don’t understand what point you’re trying to make.
Perhaps he means non academic discussions like whether vaccines actually work that you find on forums. There's loads of people doubting established facts.
Moon landing denialism is a prevalent minority belief. I think it's within the realm of possibility that the Apollo landings may one day be regarded as myth by the majority, if society (once again) takes an anti-intellectual turn. The cynical dismissal of "Hollywood faked it because of the Cold War" is a very neat and tidy meme that spreads well as it is.