An interesting addition would be some extra customization for cars "with human-like features" or just based on characters (i.e. the Mario Karts)
-Alternate textures (separate from skins) for different "expressions" i.e. when you get hit by a weapon
-Maybe the ability to use custom_animations.txt in cars as well
-Customizable sound effects that play when you cross the finish line and win/lose, when you get hit by a weapon, or when you successfully hit another car with your weapon
For those who wouldn't like something like this, it could be a toggleable option or launch parameter, much like the engine/honk sounds.
Post suggestions regarding RVGL.