Designing better cars; making parts for the 3d printers that built the cars.

What do you mean by designing better cars? How would that help?

Also wouldn't there already be an industry that makes 3D printers? Why would the car companies try to go into that business?

Give away the car for free and make money on servicing.

"Low Interest" loans

Hmm.

Open-source car development, perhaps? Could be neat.

I agree, it would definitely be neat. What would the business model be like though? How would they generate revenue?