Seeing that Sonos isn't making and does not look likely to make such a product in the near future, the answer to this may be useful for many of us as an adjunct to our Sonos systems, to take music outdoors at home or on the road.
Is there in the market today a solution that has the smartphone front end built into it? To play music from streaming services via Wifi as well as that downloaded to the unit for offline use when WiFi is missing, such that there isn't even the need for a smartphone to use it. It need not necessarily have a sim card and can do without bluetooth in this case.
Even where smart phone tech isn't bundled in, what are recommended speakers that offer battery life of 10+ hours of real battery life and sound quality that isn't a big drop from that of the play 1 units? Bluetooth of course, at this time.