I'm not usually the type to do any sort of unsolicited redesign type stuff, but I had a burning desire to illustrate a grievance I have with Spotify's current product. Just FYI - I love using Spotify, and I am happily a paying customer!
My problem with the current product as it stands today is that whenever I save music for offline mode, it doesn't go to a specific place that is easy to find. This is particularly frustrating when you run out of data for the month, or when you are travelling.
My solution to this problem is to have a section on the homepage similar to 'Recently Played', and 'Just For You' - and in the prototype I have made you can see that when a user puts their phone into airline mode, this offline playlist moves to the top of the homepage.
The prototype is available here: http://share.framerjs.com/95s0sim0brrl/
Note: I am in no way affiliated with @Spotify (unfortunately!)