A Speculative Fiction subtrope of Author Appeal, which is the deliberate creation of a future (or alternate history, or fantasy...) society in which the author's particular kink is "normal". That which is Fetish Fuel to us, is a commonplace to those in-universe.
The difference between this and basic Author Appeal is the compulsion by some authors to justify their fetish. Quentin Tarantino having lots of shots of feet in his movies is Author Appeal. If he made a movie that explains how in the year 2525 everyone will be a foot fetishist due to some social or technological development, that would be a Fetish-Fuel Future.
Used a lot in written erotica. Also some porn movies but not as much as you'd think, given that typically porn movies are Porn Without Plot and thus don't even bother with a story to the sex.
Is sometimes used to "justify" the depiction of behavior and social structures that would otherwise push the characters over the Moral Event Horizon. (Although it can still make the world crapsack or crapsaccharine, and make some people suspect that the author actually advocates such values for real.)
Sometimes characters of a Fetish-Fuel Future will consider the "normal" sexual practices of visitors to be taboo.
See also Free-Love Future.
No examples, please.