Special Note: Please note that this scenario is meant to be read as entertainment, not as an accurate prediction of the future. Also note that the viewpoints and opinions that may come across in this scenario are not necessarily the viewpoints and opinions of the author.
The bathing suits of the future will emphasize modesty over sex appeal due to a reverse sexual revolution that will be created by the nanny states of the future.
Starting with swimsuit cover-ups for women with obesity and/or visible stretch marks, the "skimpy" styles of the late 20th century and early 21st Century swimsuit will be gradually seen as "socially inappropriate;" becoming illegal in most developed countries by the year 2070. By the year 2048, bathing suits will be unisex and cover the body from shoulder to ankle. All swimsuits will become one-piece swimsuits without distinctive patterns to make it either extremely masculine or extremely feminine.
As Christianity begins its inevitable descent towards extinction, reactionary clergymen will condemn the topless men and halter top-like bikinis of the 1990s generation and the 2000s generation. It is considered unfortunate that underwear at the turn of the 21st century is modest than most swim wear so it was only a matter of time until society reacted anyway. Swimming devolves from a respectable athletic competition to a display of sex appeal and physical prowess during the early 21st century (when society was trying to rid itself of the pollution and corruption caused by the "Vulgar 20th Century."
In fact, swimming pools are removed from most major motels and resorts as more people start to gawk at the bathers instead of actually participating in the water sport.