Dude, that sounds wicked cool. I could imagine one as a battle stage where, similar to the Smash Bros WarioWare Inc stage, the players are occasionally transported to a different map where they would play different microgames, like being equipped with different items and battling each other. I would love it if there were some WarioWare characters as playable ones!
Actually, there IS a WarioWare stage in Mario Kart BUT not on the console.
The stage is called "Dimond City" based on well Dimond City in WarioWare and that stage is only in Mario Kart Arcade GP and Mario Kart Arcade GP 2. There is like many refrences to WareWare in that stage and it's amazing!
HOWEVER, it would be so cool if they could like take that stage and add it to Mario Kart 8 Delux cause I really wanna race people in Diamond City! So it would be so cool if they add that stage in in the last DLC pack!