General Motors' next-generation Zeta rear-drive platform will be heavily updated from its current form, with lots of high-strength steel to bring down weight. The price point of the cars that will use the platform makes this possible. They will include a new Chevrolet sport sedan on the shorter of two Zeta wheelbases. Think of it conceptually as a kind of four-door Camaro, even as the '14 Camaro moves to the new, smaller Alpha platform. GM is still working on a flagship for the brand, a Sixteen