One of the first decisions would be to figure out if the car is really a new Calibra or better thought of as an Insignia Coupe. The Insignia is more than 13 inches longer than the last Calibra (which ended production in 1997), and as a proper four-seater, a two-door Insignia would probably appeal to a very different crowd than the Calibra. The Insignia is already offered in sedan, liftback and wagon formats.
Then there's the matter of money: it's said that Opel/Vauxhall would need to sell 30,000 every year before making money on the cars. With fewer in-house avenues for platform sharing, General Motors' financial situation still requiring babysitting, and Opel probably about to be refused a loan from the German government, throwing another coupe into the mix might not be the go-to strategy. That said, leveraging the cost of such an endeavor while helping to augment Buick's increasingly youthful image with a Regal coupe might not be such a bad move, right?