Not sure if it's been mentioned elsewhere here yet but it seems Amazon is also tightening the screws on Send To Kindle. A "security protection for users" is what they're calling it but apparently will cause problems for people distributing & downloading freebies from BookFunnel or similar places.
https://www.androidpolice.com/send-t...liver-content/
https://goodereader.com/blog/kindle/...send-to-kindle
Now as we all know goodereader is, shall we say, a less than sterling source but on occasion they do get some things right. Sometimes. At any rate, worth keeping an eye on.