Yep, it's gonna be pretty damn expensive. But hey, so are 1/2 ton trucks, and people still buy them like crazy. And by all accounts the Canyarado sales have exceeded GM's expectations, offering a diesel obviously won't hurt sales.
Impressive towing capacity with the diesel (7700 lbs), but I'm not convinced that the rest of the hardware (brakes, transmission, etc.) on these midsize trucks can handle that much. Though if derived using the SAE-certified protocol, maybe they can? I'd like to see someone pull a 7000-lb trailer with a diesel Canyon, compared to a V6 (or even V8)-equipped half-tonne with comparable tow ratings (obviously need the appropriate axle ratios for each). How much would mileage differ? How would the towing experience differ?