The new S3 has been spotted in testing:
Audi S3 (2013) first spy photos and new A3 info | Secret New Cars | Car Magazine Online
Car's sources say that it's a 280bhp development of the current engine, with quad exhausts (bit naff IMO). Reading from other sites, it seems that they've been testing this car and the Mk7 Golf GTi together.
This just about confirms what we already knew: that the 2012 A3 looks similar to the current car and that the S3 will be at least a year later.