I'm not holding my breath. IIRC, the early reasons we were given for no Amazon Prime Video on ATV4 was lack of WebKit support on tvOS (even Bluetooth keyboards were not supported then!). So Amazon Prime Video wasn't able to go native on tvOS at launch of the ATV4. The workaround was to use AirPlay from another Apple device. That workaround still works perfectly well today for me.
After two years, it is clear someone didn't want Amazon Prime on the ATV4. AirPlay on the same ATV4 allows it to work perfectly well from any other Apple device with AirPlay support, so for me, it's been a non-issue. In addition, I have other streaming devices with Amazon Prime support (PS3, WiiU), and switching the source is as simple as a few button presses on my TV remote. No sweat.
IMHO, the lack of support for Amazon on the AppleTV is nothing short of petty on the part of one or both of these two players, especially since most folks will still be able to watch Amazon Prime when they want to, even indirectly through the ATV4.