Our best guess is that it might be a street-legal version of the R8 GT3 possibly as a last hurrah special model for the 2012 model year. This would make sense since we can see the roll cage inside the car, and some of the exterior bits fit in with the R8 GT3's aero upgrades including the vented hood and an oversize rear wing (although not near as big as the racecar). The winglets on the front fascia are similar to the R8 GT but are obviously bigger.
Of course, this could also be a test mule for an entirely new R8 model altogether, so we'll just have to wait for Audi to drop some knowledge on us before we can say for sure. Until then, check out the spy shots. Because it never gets old watching an Audi R8 testing on the Nürburgring.