The biggest rumor of the year! Several groups claim that Retro Studios is secretly working on a Star Fox title for the Nintendo Switch: one that is styled as a racing game of some sort, rather than focusing on space/air combat. This rumor has apparently been making the rounds behind the scenes in different game journalism groups, but surfaced publicly around May 14th.
Meanwhile, on the same day, Nintendo's registration/renewal of their Japanese trademark for Star Fox (and other series) went through.
While I was initially much more skeptical, it has since been reported as probably true by multiple, independent sources, including one source I trust more than most because they rarely even comment on rumors unless they at least partially verify it. Certainly, this is feasible, as Retro Studios is largely responsible for the level design in Mario Kart 7. Another wrinkle: Nintendo might actually be hiding what aspects of projects Retro Studios helps with to prevent fan outcry about them "wasting their time" on games other that Metroid and Donkey Kong.
The game is supposedly "like Diddy Kong Racing mixed with F-Zero", and "It will have an adventure mode of some kind (think Diddy Kong Racing) and there will be some boss fights and a hub world like it too."
The idea that Star Fox characters could drive high speed vehicles has already been explored by one of Star Fox Command's endings: "The Curse of Pigma". And, of course, there is a indirect cameo appearance of James McCloud (as a human-like character) in the F-Zero series, pictured above.
So, still a rumor, but looking more likely. E3 is just around the corner, so we'll know pretty soon if it's going to be shown off. Also, there's the possibility that the game could enter development, but then get canceled before any public appearance. Such a thing would be incredibly difficult to confirm, as was what happened with the LAST huge Star Fox rumor.