If you've ever used Alexa's 'announcement' feature with a combination of Sonos & Amazon products, the problem with audio synchronization between the devices is glaringly obvious.
On the other hand, I use an app called Tunity that can scan a television screen, determine which audio stream is needed, and play that stream through my phone or bluetooth headset. (It can be useful at the gym, bars, etc). The audio is rarely in sync initially, but a quick adjustment in the app allows you to make the necessary + or - correction. My point is that while the sync issue is real, it's not an insurmountable obstacle. The bigger issue, at least in my view, is that it seems unlikely that this is anywhere near the top Sonos' priority list right now.