If I was a billionaire, I’d open a auto shop that specialized in customizing normal cars into real-life Hot Wheels. A car owner could bring his or her car into the shop, show us his favorite Hot Wheels car (based on his stock car), and in a couple weeks, the shop would give him back the real-world version of his toy.
The full-size vehicle would be fully functional, but style and replication would trump street legality.
The shop would charge for the customization only as much as the base stock car sold for new. But the contract for the work would include a clause that required the owner of the car to always allow any child to get in or on the car, at any time.
If the owner can’t bring himself to accept that stipulation, then my shop just won’t make his fantasy car. No kid should ever be denied a chance to touch, climb on, or ride in a real-life Hot Wheels toy.