Okay, I read the article and wondered about this statement.
What are they talking about here? Carbon-fiber composites? Those would be difficult to dispose of.
Right now, cars are mostly steel. They rip off the plastic panels and bumper components and then crush the whole thing down. It then gets shredded and goes off to China where it is melted down and recycled.
If you start mixing metals like iron and aluminum, you'd have to separate the two before you could recycle. I would imagine that you could design the car so that ferrous components could be easily separated. Perhaps easier said than done.