First and foremost, a very close inspection of the area just in front of the rear wheel well reveals what appears to be an air vent in the bodywork. Corvette fans will recognize that a similar, mesh-lined duct was used for brake cooling on previous Z06 models, and would make a new Z07 instantly recognizable to those in the know.
Our spy shooter also speculates that the convertible top on this car might not be entirely that which it seems. Noting that when the original Z06 debuted it did so with a smaller, weight-saving hardtop that resembled the size and shape of a convertible top, our master of the long lens postulates that some trickery could be at the heart of this seemingly soft-topped tester. The convertible top seems very convincing to our eyes, however, so it's possible that the simplest answer is the true one here as well.
The wheels Chevy's development team are running on this potential Z07 are also items that we haven't seen before on a C7 'Vette. That's not proof of much, to be sure. Still, these few small changes to the car, in concert with the logical nature of a higher-performance Corvette being next on the product roadmap, fuel our Z07 dreams.
Nothing about these images shed light on powertrain details, but we do know that Car and Driver has speculated on the Z07 getting turbo power. Considering the potential for increased fuel economy and Cadillac's head-first plunge into turbocharging for high-performance, we wouldn't be shocked to see a turbo'd V8 engine, churning out 600 or more horsepower, when the Z07 finally takes its turn in the spotlight.