Very happy battle mode gets some love.
I can't think of how Mario Kart 9 can top 8D.
The only thing left is to make an open road Mario Kart game like Forza Horizon but set in different island in the various worlds of each character. (Big fan of Test Drive Unlimited here)
And then a island building editor so you can create islands to race people on; both offroad and on-road/AG. Much like Mario Maker, I think this could be Switch's surprise killer app before new Zelda comes out. It would be thier most ambitious move for the Kart series because you could remake all the tracks from previous games yourself..
There would be a budget on how many objects on the island to keep framerate high and if you want to play in low detail mode you could switch that option on for busy section/multi splitscreen racing.
Zelda went open world. Now let us see what Mario Kart would be like if they gave us Open Road street Racing game. The Wii U had Need For Speed Most Wanted. Switch needs a open racing game badly. Mario Kart is the franchise to do it. They would have to come up with fictional Mario Kart road vehicles and fictional makes and models. And there would be a Death Race type mode where weapons are allowed and the Karts are modified versions with armor and engine upgrades for battles while racing. (think of cartoons like Spped Racer where getting people to crash is perfectly ok and you can jump over obstacles and saw blade others to crack their armor and damage their vehicles. (no balloon. It's the vehicles that you attack) Every character has their own fave make and model that suits their personality but you can switch models and makes when needed. (bowser's vehicles have spikey armor, princess peach can float in the air longest after a jump, Mario's can jump-dive-butt-stomp and bounce off the roof of other cars to overtake them, yoshi's have the best flame weapons etc)
Within the world are Crazi Taxi styled missions to earn money and get to know the streets in free-roam mode. There are hidden vehicles in the environment that can be found and you can build up vehicles when you get the parts hidden in the world. This is nintendo's answer to Test Drive Unlimited and Forza Horizon but with some Crazy Taxi and GTA thrown in. The technology is good enough to maybe even create procedurally generated maps to explore inside the vehicle (no man's sky) and have race that span entire country and go on for weeks. (players set the checkpoints on each planet) Mario Kart is great for short race but what about long races that stretch from island to island? Your kart transforms into speedboat form when you got to cross the sea from one island to the next - finally waverace fans can stop complaining that they were left out when Mario art 8 catered to F-zero fans with AG vehicles forms
The emphasis of procedurally generated cross country mode is the beautiful scenary you can't get in the normal hand crafted islands. The experiences is closer to "Out Run" where you will see more variety in the places you race in but they are remote areas so you will see wildlife, farms, sealife (whales and dolphins if you are in speedboat mode) and the time of day changes so you will be fighting the darkness and weather conditions. (sandstorms and wet weather which may alter your ability to pass through sections easily (eg snow may cause you to have to slow down, mudy areas may bog you down etc) The advantage of doing the long races is you get to see better sights like racing up and down mountains and this would be interesting for let's play streamers as it is all randomly generated.