The argument about being able to load Aple Music onto a Nano and then cancel the subscription is specious. I could just as easily buy a 64Gb iPod touch, fill it with music, turn off wifi, then cancel my subscription and keep all the music. Or do the same with a Mac, loading hundreds of GB of music onto an external hard drive and never using it when I'm connected to the Internet.
I like to take my Nano to the gym, the beach, out for a jog, anywhere I don't want anything as bulky and expensive as my iPhone, iPad or MacBook. Why shouldn't I be able to?
The whole point about Apple Music is finding new music, so most people will connect their Nano to iTunes regularly to freshen their music. This gives plenty of opportunity to implement short-lived DRM licenses that get freshended on reconnect, so Apple could protect the artists against offline hogs by making the license expire after a month or two. Of course, you'd then have the problem of people changing the date on their Nano.
All in all, there are more people out there who'd use it properly, so why penalise them to protect against the minority who would abuse the system? They're probably too busy ripping music off YouTube anyway!