Long ago (late '80s-early '90s), I occasionally listened to a "Smooth Jazz" radio station, CD101.9 in NYC. Worked as background music.
I got the impression that "Smooth Jazz" as a genre has been pretty much absorbed into the broader genre of "Adult Contemporary". Not sure what AC exactly is, though...seems to have overtones of background/bedroom music.
I can see a book chapter or section on smooth jazz. I'd actually be interested (to a degree) in its history and development.