TV Remote Analogy
"Imagine if your TV supplier sent you a message saying your remote control would no longer work once the TV software was updated?"
This is a false analogy. The reality is more like your TV manufacturer sends you a message saying your old remote control will no longer work once the TV software is updated but you can pick up a new one from your local electronics store free of charge.
Sonos do not make iThings only the control app that goes with their overpriced audio equipment. You may well find that the reason for this change is that Apple are forcing their hand. Or that they want to use iOS features not available in the old versions in order to give you a better experience.