@KayOhtie Yeah, I do this too now, except with Calibre as the destination instead of (presumably) an intermediary step of this. It's niiiiice.
The one Amazon feature that I wish had an analog is Whispernet. I know you can just use wifi, but being able to send books, magazines, and serialized RSS to myself over cellular was... very very handy.
@Goldkin DeACSM is the plugin that lets Calibre be the destination for the encrypted book ^^ I just transfer to my kindle over USB, if that's what you meant