That’s where I’m getting conflicting info: I understand you won’t be able to “download and transfer via USB” from the Amazon website but when you download a book from the Kindle over wifi it’s still a file on your kindle that can be browsed to if you connect your Kindle to a computer via USB

Then you copy that downloaded ebook (.kfx) to your computer and import into Calibre and use the Kindle plugin that strips DRM from .kfx files.

I’m going to try that today and see if it actually works…