Apple's Project Titan—dubbed Apple Car by the media— is widely reported to be all about automotive technologies. The latest rumor involves a partnership with BMW, specifically for the carbon fiber bodies used in the BMW i3. Manager Magazine (Google Translated):
The German automaker BMW and the Californian technology company Apple have negotiated a far-reaching cooperation. Apple was interested in the body of the BMW i3 electric cars, Manager Magazin reported in its latest issue (release date: Jul 24th). Company CEO Tim Cook was considering to use the BMW model platform for a car project, they say in the business environment. First negotiations in late autumn 2014 but were broken off. They had agreed to keep talking and to check the views from time to time together.
The i3's materials are as exotic to the average driver as the powertrain. It is a BMW, so they are very nice materials, but it's unusual to get in a car that has fibrous recycled plastic door and dash panels coupled with an undulating band of open pore eucalyptus. The exposed carbon fiber monocoque shell (instead of a traditional welded steel frame, the i3 uses a single-piece molded and fused carbon fiber shell) is balanced against a wool-and-recycled plastic blend.
Regardless of whether or not this rumor—or partnership—pans out, Apple industrial design is all about materials and I'd expect anything they put out to be as innovative in construction as it is software and integration.
We likely won't see anything official for several more years, but it'll be interesting to watch in the meantime.