I saw more recent spy shots of an impreza mule with a hood scoop grafted on, indicating turbo.
My guess is they're doing drivetrain testing using the Impreza chassis. Remember the BRZ mule we saw at the very beginning that was basically a chopped up Impreza coupe? looks wise it's nothing like the production car so there's every possibility that the WRX will look quite different than the current Impreza. There's a reason they haven't moved the current WRX/STi to the current Impreza chassis. If they were going to do that they would have released them concurrently.
For the record, I quite like the new Impreza for what it is. A very practical, above average econobox.
Nathan