No need for forgiveness! (Unless you are Jeff Bezos).
It could have been iOS 11 itself.
As someone said above, Airplay is not really a solution for Prime Video. AFAIK, you've to keep the app open on your iPhone/iPad. Not a solution for me.
Airplay 2 is mainly about multi-room audio, improved latency and buffering, so Airplay can be better used for wireless speakers.
I have a couple of devices now supporting Prime Video (PS4, X1, Shield, FireTV Stick Basic Edition), but Apple TV is preferred because the UI is so much smoother and you can easily power it on/off with a Harmony remote,
Looks like Amazon is really going for "before the end of the year".... so my guess December 31st 23:59
On the other hand, The Grand Tour starts again December 8....