The first one came from me thinking how it would be fun if they made some kind of reference to the OG movie in the new one, the rest are general Mario doodles :]
I love when everyone in a community unanimously adopts a certain headcanon because it's just that good. One of my big favorites is Luigi being a mechanical expert and gifted engineer. 👏
I also very much agree with @pianokantzart on the fact that the man should have his chance to build/repair karts. I feel like he'd be a magician with those! 😄🔧