Finally! Amazon should have done this long ago. ePub v3 supports everything MOBI does and it has really extensive support across platforms. This is HUGE for people with a big eBook collection.
Previously, you could send a MOBI file to your Kindle email address, and it would be delivered to your Kindle. Now, you have to send them an ePub file, and Amazon will convert it to an AZW3 file (which is structurally very similar to MOBI) and send that to your Kindle.
If you have an ePub file and you want to read it on your Kindle without going through Amazon's servers, you have to convert it to AZW3 (or MOBI) yourself, either using Amazon's Kindle Previewer GUI software (only available for Windows/Mac) or by using a third-party tool like Calibre.
> Amazon has announced the retirement of its proprietary MOBI file format for eBooks, and a transition to the EPUB format for use on Kindle devices and apps.
which makes me wonder if they know more than we do?
Still it's a good thing to move to a common standard to simplify things.
Kind of like us devs that have to deploy code for various platforms, which is arguably an order of magnitude more complex in some cases. You're lucky that the Kindle doesn't support 3 OSes with each its own proprietary formats lol.