I'm not sure if this has been mentioned before (I kind of think it has, but I can't find it).
I purchased a Kindle ebook today and was directed to a new beta Library page called "Your Books":
https://www.amazon.com/your-books
I'm wondering if this will eventually replace the Content & Devices page.
I am hoping not as this Beta page lacks a lot of functionality, including Download & Transfer via USB.
But this may be how Amazon gets rid of Download & Transfer via USB.