I'd love to see a nice combat pump or semiauto shotgun from S&W. I'm guessing they'd just put their name on someone elses, like they did with their AR-15 (Originally a Stag IIRC)
I think an 870 with a knoxx stock, an integral upper rail, and mounts for a light would make a great M&P 12. Assuming the quality was what i'd expect from the rest of the M&P line, i'd consider it if the price was right.