I think this would end up sitting the draw next to my camera. For me phones are "good enough" for music given I'm mostly listening on the go so there are many more factors that influence the sound.

The best audio player is the one you have in your hand right now. (to butcher the quote) And that for me, just like my camera, is the phone that is always there.

Having said that Music, like coffee, or keyboards is a very personal thing that people connect with and so I can see the appeal of the focused device. It's similar to the e-book reader I suppose where there are not the distractions of a full connected phone. Just you and the music.