Recently uncovered patent suggests Sonos is working on a pair of headphones
Amazon.com: SOINTONE HFF86 Wireless Headphones for TV Watching with Bluetooth Transmitter (Digital Optical AUX RCA), Pass-Through Support, Over Ear Headset for Seniors, No Delay, 40Hrs Playtime, 164FT Long Range : Electronics
Sonos wireless headphones detailed in patent - CNET