Once upon a time, a guy was interviewed and merely said that Model ☰ would be made from 'appropriate materials'... Sometime later, someone asked Elon Musk and in an offhand comment he said it would be 'made of steel'... Since then, many Tesla Enthusiasts have predicted the Generation III vehicles would be built primarily using 'high strength lighweight steel', with strategic use of aluminum bits, and perhaps combined with a carbon fibre reinforced plastic 'life cell', similar to what BMW introduced with the i3/i8.
Even so, at least until Thursday, I'll hold out hope the Model ☰ will be built in a manner very similar to the Model S and Model X. That is, 90% of frame and body being aluminum. So that most of what you see in the exterior of the completed car is aluminum, plastic, and glass... While some critical components that are hidden within the body are made of hardened boron steel. I believe that the long-term anti-rust aspects of construction greatly outweigh the issues of fender bender correction.
Well, I don't see this so much as 'competing' with Accord, Camry, Malibu, Altima, Sonata, and Optima... So much as showing the Model ☰ is a suitable 'upgrade' from those vehicles. The AUDI A4 might be considered an upgrade from the Accord -- until someone realizes the same car can basically be had as a Volkswagen Jetta -- for about the same as an Accord. And let's face it, the combined A4 and Jetta sales doesn't come close to those of an Accord in the US. On the other hand, if 40% of Model ☰ sales are in the US, and 500,000 units are sold worldwide, that would make for 200,000 units sold here each year. Well above what BMW 3-Series has ever managed to accomplish. Dependent upon just how popular the Model ☰ becomes in the US, and when manufacturing facilities are built in Europe and Asia to make them, it could well be that it reaches 200,000+ units per year here well before 2020. And that would be more than enough to crack the top twenty passenger cars sold here in just about any year.