Hi @Tek_Freek 

This of course is neither an official response on behalf of Sonos nor any derived from investigation of any sort. Just my opinion. 

I would consider the use of  band width by the Alexa Sidewalk (AS) feature no different than placing products on your network which could potentially siphon band width from your Sonos. The overall effect may or may not be of note. 

What the Alexa Sidewalk feature does IMO is similar to what PlayStation 3 users did on a voluntary basis to allow their units to be accessed during non use to allow access to the CPU as part of a processing collective for medical research. The AS feature to my understanding will use the siphoned bandwidth to create a community bandwidth to keep Alexa units online even if they lose connection temporarily to the home router/modem.

My concern is not so much about affecting Sonos but more importantly network security. The potential for a weak link to cause a breach affecting all connected nodes IMO seems to great to ignore. I have disabled the feature in my Alexa app.

I wonder what others have to say on this subject

BTW...I would suspect Sonos products in wired mode to be somewhat immune. JMO.