It's a fait accompli Aston Martin and Porsche are launching a pair of low-slung, coupe-like sedans — the Rapide and Panamera, respectively — and whispers of a similar BMW peaked on arrival of the company's CS concept. Does that mean a new sub-class of touring sedan will be the latest must-have for sport-minded automakers? Probably. But a four-door Corvette? This week, Automotive News's Rick Kranz makes a case for Chevrolet to join the four-door coupe soiree by limo-izing its signature sports car. Purists would balk, he says, just as Porsche devotees will likely roll their eyes at the Panamera (though they've already had their first fainting spell with the Cayenne). And he even quotes GM's Bob Lutz as making the connection between the Porsche and Corvette brands, though no plans are in the works to follow its lead. What's more, if GM ever did stretch the 'Vette platform, Kranz says, it could be used for a desperately needed Cadillac flagship. But while it's not a completely hairbrained idea, we're going to have to side with the purists on this one. But the Cadillac? That's the one to build.