"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".
Reported on Eurogamer, a new round of rumors from Reddit and image boards suggests that Retro Studios has been working on a project titled "Star Fox: Grand Prix", a sci-fi racing game said to feature elements of Nintendo's own F-Zero with an action game twist. The arrival of a new form of Star Fox could signal some new popularity for the series though, and that's worth a celebratory barrel roll no matter what.
The last title from the studio was the excellent Donkey Kong Country: Tropical Freeze on Wii U, which recently saw a re-release for the Nintendo Switch. The secretive Texas-based developer has been a favorite amongst hardcore Nintendo fans since bursting on the scene with Metroid Prime, but they've been even more quiet than usual since shipping Donkey Kong Country: Tropical Freeze in early 2014.
Nintendo nor Retro have given a reason as to why they weren't working on Metroid Prime 4 after developing the first three entries. Something like Diddy Kong Racing mixed with F-Zero essentially. So completely different to normal F-Zero and with seemingly nothing in common with any previous Star Fox game. While no specific details about the potentially scrapped project were revealed, it allegedly "went through a rocky development cycle".
There's been substantial skepticism of Star Fox Grand Prix by commenters. While others are wondering why this is a Star Fox title and not a new F-Zero.
Keep your eyes on the Mammoth Gamers for further developments on the next probable Star Fox game.