The rumors are this game is like Diddy Kong Racing which is why they would have picked Star Fox over F-Zero. If you're going to make a game that has a mix of flying, ground, and water vehicles, as well as Boss battles, the Star Fox franchise fits that gameplay much better. Hell I wouldn't be surprised if Retro manages to incorporate some traditional Star Fox action into the game, especially in the single player so even though the game is technically a racing game, some races will almost blend the line between racing and rail gun shooting.
I know we haven't had an F-Zero in a long time but if this Star Fox racer is indeed going to be channeling Diddy Kong Racing with a full fledged Adventure mode then I'd easily take that instead. We could potentially be looking at one of the most unique racing experiences in decades if not ever.
This is why I find it funny how some act like Retro's talent is being wasted when making a unique high quality racing experience sounds like a good use of said talents. Hell, during the N64 and Gamecube era, Racing games were literally one of Nintendo's biggest genres. Compared to last gen where Mario Kart was literally it for racing, and we all know the complaints about lack of meaningful single player in it. So to get a new racing game with a meaty and unique single player content sounds like the perfect thing Nintendo could use Retro for if you ask me.