As somebody who doesn't use Spotify, I wonder how open the Core will be, e.g. for other audio providers like PocketCast. If I could just tell it to play the latest podcasts from my PocketCast, this would be the perfect fitness tracker for me.
Oops, now I see what exactly the core is... Maybe a bit different.
Besides that they say the Core runs "unlocked" Android 5.0, so I'd imagine you can load it up with whatever you like.