Sonos have had a form of AirPlay support for quite some time but frankly it has always been a disappointing kludge even if it got the job done. For those unaware the current and only
solution involves buying an Apple AirPort Express WiFi basestation, you then connect the audio output from the AirPort Express to the audio input on a Sonos device. You would then AirPlay stream to the AirPort Express and it outputs to the Sonos.
This of course means spending more money for an AirPort Express or even several but also adds an extra device in the link with the possibility of additional overhead and small audio quality loss. In reality it was 'good enough'.
Unfortunately Apple have just discontinued both the AirPort Express and the AirPort Extreme. (The Extreme could not do this as it does not have an audio output.) No other device has ever offered this functionality. This means that going forwards it will effectively be impossible to use AirPlay audio streaming with Sonos. (I can see the secondhand prices of AirPort Express devices on eBay going up.
Therefore it is time for Sonos to solve this problem properly
the way they should have done it in the first place which is to provide built-in support for AirPlay in their systems. Many AV Receivers e.g Denon, Yamaha, etc. have built-in AirPlay support as do other brands of wireless speakers e.g. Bowers & Wilkins. Whilst I believe most if not all of these are doing it by including a hardware chip with official AirPlay support the AirPlay protocol has been reverse engineered and open-sourced and implemented in many software programs purely as software. I believe the original need for the hardware approach was to include support for FairPlay protected music tracks but as iTunes music has not had such protection for many years and there are various legitimate approaches for upgrading your music to remove such FairPlay protection using a software only approach without FairPlay support is a realistic solution. (Obviously AirPlay Mirroring is never going to be possible with Sonos which is an audio only device so the fact you might need to stream FairPlay protected videos is not relevant.)
One could argue Sonos' previous short-sightedness is now coming back to bite them and if they had previously added this AirPlay chip when designing the new(er) Play 3, Play 5, etc. devices then most of their product line would already be compatible. (The older Sonos Connect devices might predate this.)