I agree with the track builder idea. So here ꧋is a list of things that I would put into the game (if it was up to me)

1) Track Builder

2) In Battle, after l𓆏osing all your balloons have the driver tu🌄rn into a bomb kart again like in MK64.

3) Bring back "the Double Dash concept" but have it be able to be flipped on and off in t𝐆he options menu.

4) Custom Cups (most cups have only one or two tracks I actually like so it would be nice to form cups that includes all four tracks that are to my liking) (and yes, allow the tracks to include♒ custom tracks as well)

5) Includeꦗ mandatory pitꦯ stops. To refuel and get tire changes.

6) After the races are over with. Repairs need to be made to the karts (or♍ particular body style) and the engines before they can be used again. Collected coins can be useꦅd on these.

7) If that is true, a💯bout the 24 racers at one time, then have the number of racers be able to be adjusted between: 8 (like in MK64 & DD) 12 (like it's been since Wii) and 24.

8) When it comes to ꩵracers do like what was done in Smash Bros. Ultimate and bring back ever🃏y racer that has ever appeared.

9) When it comes to stuff that🐲 can be added to the custom tracks Nintendo should take a few pages out of the Little Big Planet Karting playbook as well as𝄹 borrow some ideas from what they did in the Zelda:Link's Awakening Dungeon Builder and let players take parts from tracks they already raced on.