Filed under: BuickNow that General Motors has decreed that Buick will be one of its four core brands, its lineup will need to be fleshed out a bit. The Lucerne is going away momentarily and the mid-size Regal is on the way. However, that still leaves only three models, including the LaCrosse and Enclave. Earlier this year, GM took us on tour of the Buick design studio and showed off a six-vehicle lineup for Buick, with a new compact sedan as the entry point. That sedan is essentially just...