I use Spotify a lot and I will love to have a Spotify channel for my daughter with all her favorite songs.
That sounds like a good idea in theory, but personally I feel that using the Relays as a music playing device is not the best for children as they may end up wasting the battery more than parents would like?
A Relay last for 2 days, if will have Spotify I think will last all day. I am trying to teach my daughter to chatge her Relay every night.
I have my own Relay and I will love Spotify on it since I do not have any mp3.