Theory: Mario Kart 8's in 2014

Abstract
Mario Kart 8/Mario Kart 8 Deluxe takes place in the (in-universe) year of 2014.

Arguments

 * Argument 1: Sponsors such as the “Toad Polar Expedition 2014-2015” seem to suggest this is the current year.


 * Argument 2: A poster in the Water Park track shows the history of the Submarine in the Mario Universe, with the first model being created in 1987 and the newest model seen in Mario Kart 8 being created in 2014.