While I agree it boils down to Amazon missing a delivery window, but it's Apple that's on the hook with their customers. I, and many other, bought the ATV 4K in September because they said the app was coming "later this year". If they don't deliver at all, that's ...
You seem to be putting a lot of energy into deciding how upset to be if it doesn't come out this year, but it remains that Amazon (and Apple) are still well within the delivery window they mentioned. If the cable company says they'll be there between 3 and 5 and the guy shows up at 4:30, do you yell at him because you thought he was going to be late? I'm anxious to get the app too, but maybe wait until they actually miss the window before getting too worked up.
No. At least not with the current batch running iOS 11. Maybe the 8 or X will? So far, I've not even been able to confirm it will stream 4K video from a Mac using iTunes Home Sharing. It streams, but it doesn't look like 4K to me. Maybe after 11.2 and the ATV switches automatically to the video format, I will finally be able to use the TV to determine the actual source formatting streaming.