[stunt]

You can still use other formats on your Kindle. That restriction is for publishing new books on Amazon store.

If you want to publish a new book on Amazon, you have to use EPUB instead of MOBI. That's the only change afaik.

[innocenat]

No, this applied to Send to Kindle service too. Announced a few days ago.

https://www.amazon.com/gp/help/customer/display.html?nodeId=...