Besides the overwhelming plethora of implicit evidence of the future through various advances in technology and ZUN's thoughts about what the future holds in general (which is a massive overarching theme throughout the works), we have some more explicit mentions to historical things that currently exist rather than merely stuff we'd think of as futuristic, which includes Mt Fuji having been extinguished and designated as a World Heritage Site, and cars being touted as an outdated mode of transportation. They also talk about Stephen Hawking in the past sense, so there's that.