Mr Wolfe, summing up your arguments as I read them, you seem to want digital purity of some sort; to finally rid the world of the evils of Mobi and make everyone like what you like better. And if the price of doing that is huge inconvenience to a lot of readers, well that's just life in the digital age.
I think Amazon is to be applauded for sticking by their old customers as well as they can. Good for them. It's not that I'm against digital purity, I like nice clean bits as much as the next guy. But that's not even a close second to everyone being able to read the books they bought on the devices they bought to read them on.
I mostly read on a phone using Moon+ so I mostly do read epub. But I do have a couple of new Paperwhites that I bought just before I started using the phone. If Amazon took your advice it wouldn't affect me much; if at all. But I'd be very disappointed in them.
Oh, and half the people in my retirement home do have older Kindles that still get Mobi files when they download their books. They'd be devastated. Some are avid readers. None has any way to convert books. Mine isn't the only computer here but I'm the only one here who knows how to use one. Your purity would sure take a big chunk out of my free retirement time.
I just realized that it sounds like I'm arguing against some kind of racism. I realize I'm not doing that because I know you better than that. But it sure is a close parallel.
Barry