Why is Mario Kart World not called Mario Kart 9?

There is a reason why Mario Kart World isn't called Mario Kart 9. Despite the often typical naming convention for the series, Nintendo wanted to go above and beyond with this game, which is why it decided to forsake a numbered approach and to instead commit to a more unorthodox name akin to former more significant leaps in the series.

Speaking about this in an Ask the Developer article, producer Kosuke Yabuki explained the reasoning to co-title the game as 'World'. He said in full: "If the idea had just been to add more courses, then I think we would've called it Mario Kart 9.

"But, that wasn't our approach this time. We wanted to take the series to the next level. So, we decided to drop the numbering this time and go with a completely new title, Mario Kart World. So, we'd already added "MARIO KART WORLD" to the concept art from the early stages of development."

He went a step further to add: "In previous Mario Kart games, after finishing a course, you'd move on to the next course. However, I thought that with modern technology, being able to seamlessly transition between courses and realize a single, vast world wasn't beyond the realm of possibility. So, with this in mind, we set out to create a new kind of Mario Kart....And that's when all our troubles began."

The team then goes on to explain that this idea of stepping up the franchise instead of simply adding or tweaking established gameplay came from the mindset that they had already achieved everything that there was to achieve in former Mario Kart games. In fact, planning team lead Shintaro Jikumaru worded it in quite a clear way.

"I also felt that with Mario Kart 8 Deluxe, we'd pretty much perfected the formula of a Mario Kart game where each course is played separately. In that sense, I felt that a Mario Kart game where you play in an interconnected world would also be rewarding from a developer's perspective. However, from a player's perspective, it can sometimes feel particularly disappointing when a sequel changes too many things. So, as someone involved in game development, I felt that our first challenge was to figure out how to add new elements while still making it satisfying for those who've played previous Mario Kart games."

So, don't rule out a return to a numbered naming convention, perhaps for Mario Kart 10 or X down the line, as maybe by that point the series won't require a massive leap forward in ideas and concepts, and will be fine with simply new tracks and features.