I think if they do, it will be able to link up with your copy of Mario Kart 8 Deluxe and be able to share content between the titles. My running theory is that there is little more to evolve with Mario Kart beyond 8 Deluxe, but they could throw in some unique gameplay mechanics to make it standout from 8 and make a case for being a separate game and not just DLC. Let's take for example if they bring back the Double Dash formula for 9 while still looking like 8 Deluxe overall. That's cool, 9 could be all Double Dash. But, if you have 8 Deluxe, how about they give you the ability to share content between the 2 titles, all the karts, racers, and tracks. But then, you could also choose which style you want to play each track in: standard 8 Deluxe format, or the Double Dash format. Suddenly, every track between both games can be experienced in ways that they couldn't initially in the game they were originally released for. Same goes for items, now you could choose to play with the 8 Deluxe item set, the 9 item set, or the combination of both item sets (assuming there would be different items in 9). It'd be a smart way to encourage players to get both games, while both titles could also exist as their own title in their own right without linking up. Guess in a sense, it'd be like a modern version of how Sonic & Knuckles could combine with Sonic 3.