If GM does offer the V-6 it would likely be in premium models like Cadillac and maybe Buick. Since Saturn is now the effectively the US branch of Opel and has been largely Europeanized, it would also be a logical home for diesels, especially in the Outlook crossover which is pretty thirsty with its current gasoline 3.6L V-6.
GM will be showing a diesel variant of the E-Flex system in an Opel body shell at the Frankfurt Motor Show in September and reportedly will also put the same powertrain in a Saturn Aura for the January Detroit Auto Show.
Update: After talking to a spokesman at General Motors, it appears that most of what Automotive News wrote and everyone else is repeating is pure conjecture. For the time being the 2.9L V-6 is a Europe only engine set to debut in the 2009 Cadillac CTS. There are currently no plans to bring this engine to the US market. Of course depending on what happens with regulations (both fuel economy and emissions) and market demand, plans can change. All work on the E-Flex architecture is being done on the Global Compact Car platform (currently known as Delta) and the Aura is built on the larger Epsilon mid-sized platform. With the Saturn/Opel tie-up a Saturn diesel E-Flex is not out the question, but if it happens it will be on something derived from the Astra.
[Source: Automotive News - Sub. req'd]