You have intermixed to different topics here.
Alexa Service - Amazon still working on abilities here. Anything Alexa voice service is controlled by amazon. They just added Deezer support. I don't forsee Amazon ever adding local stored music ability to the voice service. When it comes to services or abilities here then Amazon is the one to question.
Audible - lots of leaks and most expect it to launch by mid-march (next Tuesday we hope)
Google Assistant - different voice service. Most expect we will see mid-summer.
Apple Airplay2 - Apple still hasn't figured this one out enough to put on their own speaker. Once Apple gets their act together and actually gets Airplay2 working properly we would expect about 3 months later for Sonos add it. I would have earlier predicted summer. But with Apple still struggling to get it right I think Sonos implementation is probably looking like Sept-Oct time period.
Respect the Queue (2)Move (3)Beam (1) Era100 (2)ARC (1)SonosOne (1)Playbar (4)Play5 (4)Play1 (3)Play3 (1)Port (2)Connect (1) Roam (2) Ace (1)Connect:Amp (4)Sonos Amp (1)Sub + (9) Echo + Smartthings; (2)Play)