If Apple Music was designed to make people to listen to music then iPod Nano/Shuffle should've been part of it. Having Apple Music is great but only if you use your iPhone or iPod Touch, but in my case I use an iPod Nano to listen to music while running or working out. In other words I would end up choosing one plan either to be involved in Apple Music or not .. I guess its that simple but again there are probable possibility of having the Apple Music run on your iPod Nano/Shuffle, just a matter of decision making.
Apple Music was designed to compete against other Music services such as Spotify, Google Play Music, Groove (former Xbox Music) and soon Facebook Music and since none of them are available to work on shuffle or nano (hence wifi not available) then Apple decided to exclude them from that option.