I think there should be an Rc-car. It is a smaller, faster, more stable version of the jeep. The Rc handles most like the BMX bike where if you land while pedaling (on the throttle) you can flip. It also should be super affected by the boosts since it is smaller and lighter. Looks roughly like this:
man i loved the unicycle in the original games... i think itll fit well nowadays, its like it was made for spacebarring