I tried to make a little mod. Scraping all sound files from Crystals Car Addons, plus some additional engine sounds from other games.
All karts sound different now.
Video Link to Vidlii (beware): https://www.vidlii.com/watch?v=yztqpQP7_OC
I value the audio experience in a game quite high. Knowing, a Gavroche is approaching from behind, those little details make the world more relatable. What do you think about it? Would you consider giving every kart its own sound?