I'm really curious what the status would be of third-party content applications. Let's say that Amazon exposed reading functionality in a Kindle Web API but no

I'm really curious what the status would be of third-party content applications. Let's say that Amazon exposed reading functionality in a Kindle Web API but not purchasing functionality. So I implement an iOS application called kReader which can read Kindle books. I wonder where I'd fall in Apple's rule restrictions then, since I'm not offering anything for sale either in-app or out-of-app.