Keep in mind, this is not an effort to *sell* a car. This is a research project exploring the limits of what's possible. As the man in the video says, there are lots of ways to create cyclical manufacturing, and biodegradable products would be one idea along with recycling and so forth.
Also keep in mind that biodegradable != compostable. You can create a biodegradable product that only degrades under specific conditions (either long time scales, high temperatures, etc). In fact, biodegradable is a slippery term in general
