I mean, given that Calibre can convert from anything to the reader's native format I couldn't care less what kind of format any eBook I get is in, as long as it's not PDF.
Still it's a good thing to move to a common standard to simplify things.
as a self published book author, i have to worry about formats that my readers use to give them the least hassle. unfortunately kindle is 1/3 of my readership.
Well if you're selling you really ought to provide it in all available formats, especially with how easy it is to convert between them. Should take you a total of what, 10 mins?
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.
the devil is in the details. try getting formatting/images/code displays right on all 3 platforms when the test/iteration cycle is minutes. not saying this is the biggest problem in the world, just explaining why even if amazon discontinues mobi i still have to support mobi.
Still it's a good thing to move to a common standard to simplify things.