With Jaguar, Audi, and BMW having both SWB and LWB versions of their flagship sedans in the US, I think MB is remiss not to bring over a SWB S-class. (I actually didn't realize they made one before reading this thread...) I think plenty of people would go for them. I know my dad would be happy to get a SWB S430 4matic, for one. A SWB S430 would become the top-selling S-class model, for sure. Probably take a good amount of market share from those buying the 745i, too.
The short (standard ) wheelbase S Class is sold in Canada. It is about $7500 less than the long wheelbase. If sold in the U.S., I would have purchased that model, however MBUSA deprives us of the choice.