The concept is (and the future A7 will be) built over the A6 platform. This is a modular architecture called LBK, which allows changes in lenght, width and height, according to what Audi wants the car to offer its customers. It is a concept Fiat has already used for Stilo. Bravo uses the same platform, but with the changes the Italian carmaker thought that were necessary for the new hatchback.
Considering the Sportback Concept will be presented this year, we can expect the A7 to be presented in no longer than two years. Fans of the concept will be able to buy Audi's four-door coupe by 2011 or sooner (so we hope).
Source: Fourtitude via Autoblog