I was playing Mario Kart Wii just now while thinking about old Magical Girl shows (thanks to a certain someone) and my brain just merged them together into this thought that made my heart explode into rainbows.

That would be the best thing ever. A racing game featuring classic Magical Girls like Minky Momo, Creamy Mami and Persia/Pelsia/Perusha/Whatever. 

Each one would have a kart based on their batons or whatever something relevant to their shows (like the crepe stand in Creamy Mami, or the red car in Minky Momo that has the propeller on top and attaches to the van thing) and they would pick up little magic crystals on the road that let them use their powers to either attack each other, or give themselves an advantage (like flying over parts of the tracks)

There's a cruel irony in the thought of Minky Momo racing down the road in a car and running over other young girls.

I want this to be a thing so bad now

you could even have like a rivalry sort of story. Like throw in Toei animation Majokko (Sally, Megu, Honey, etc.) vs. Pierrot & Studio Reed (Momo, Mami, Emi, etc.)

This reminds me of an idea I had for some kind of anime equivalent of Super Smash Bros.