Newegg.com's product description of Mario Kart 8 suggests that the upcoming racing game will be the first in the franchise to include a track editor.
The listing reads, "It [Mario Kart 8] features new elements such as customizing bikes and designing your own tracks." Also helpfully pointed out is the fact that it's a "new game for the Wii U" and, in case you couldn't guess, Mario Kart 8 is a "sequel to the game Mario Kart 7."
Nintendo has not yet announced any such feature for the game and have yet to respond to requests for comment on the matter but the company has previously said that karts will be customisable just as they were in Mario Kart 7 on 3DS.
Mario Kart 8's product listings on Amazon, Target, BestBuy, and GameStop make no mention of a track editor. The game is set to be released on May 30th and could make use of the GamePad for creating tracks.
It was recently announced that the Koopalings will be playable racers in the game.