NeoGAFs Kent Brockman
The latest rumors surrounding the next Mario Kart game suggest that it will be titled Crossroads and will be a crossover game.
According to Twitter account LeakyPandy, it's possible that a new Mario Kart game could be revealed in 2022 that will either be called Mario Kart 10 or Mario Kart Crossroads. Some Mario Kart fans may be confused by that proposed title, as there was never a Mario Kart 9. However, it seems that if there's any truth to this rumor, Nintendo must count the mobile game Mario Kart Tour as a main series entry and therefore it would effectively be Mario Kart 9.
The other interesting tidbit about a potential new Mario Kart game is that it will apparently feature multiple IP. The Mario Kart series has stuck pretty strictly to Super Mario characters until the latest entry, which introduced Animal Crossing's Isabelle and The Legend of Zelda's Link to the mix. It would make sense for the next Mario Kart game to explore that idea further and add even more non-Super Mario characters, though fans should keep their expectations in check. No concrete evidence for a new Mario Kart game has been presented and it's entirely possible that there's no truth to this leak.
there's no evidence to back up these claims, and so it's best if fans take this information with a massive grain of salt until an official announcement comes - if one ever does.