Buick wouldn't have worked from the NASCAR branding angle, though. They already have the LaCrosse for their large soft-lux car. A variation of the LWB Zeta (Caprice PPV here) is sold in China as the Buick Park Avenue...
I've read that Buick is getting a Riviera 2dr in a couple years as a halo car, it may be on the new Alpha RWD platform which the ATS, next Camaro, next CTS will use..