I'd really like to have the opportunity to have more than just 3'333 offline songs. I think you should create a "gold" and "platinum" membership that allows users to get more songs on their devices, paying respectively a higher monthly fee. For example $20 for 10'000 songs and $30 for 20'000 songs, this way I'm never ever going to need to update my iphone library again. I'll just have everything I need with me. That's perfect for long car trips for example.
The thing that I most hate about doing that with itunes is that a lot of the mp3s I have dont have the proper names or album covers, spotify makes it a lot easier without having to spend a fortune on digital files (which I honestly don't lay much value on, I rather pay for the whole real thing: CD + booklet etc.)
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