FYI They have publicly said they have no plans to roll it back. 

Suddenly finding I’m unable to link to my own NAS (on LAN) server is the final straw for me. I was about to extend and update my Sonos system but now, with their app screwups and inability to acknowledge their mistakes, I will be investing in an alternative system.

Be sure to come back and let us know what system you can find that allows the use of SMB v1. 

Hi Airgetlam,

I already have a Yamaha HiFi with MusicCast so I’ll probably replace my Sonos speakers with Yamaha ones and use for my home music system. I have a few Sonos units which sound great but all I want to do is stream my own, purchased, music… I’m not really interested in streaming subscriptions. I’d be happy just being able to continue with the old app but with Sonos that isn’t an option :-(

Sonos has not eliminated streaming your own, purchased music.  They simply no longer support an outdated, (supposedly) insecure sharing protocol, SMB v1.  All you need to do is get your library using SMB v2 or v3 and your ability to stream your own music will be back.  There are literally dozens of threads here which will tell you in great detail how to accomplish this task. 

Same exact issue, ridiculous.  Ok - I finally got my system back.  Customer service was a joke - this worked for me.  I literally factory reset every speaker one at a time and re-added them to my system 1-by-1.  Then re-set up my home theater, re-calibrated all my speakers for each room, etc.  We have 10 Sonos speakers throughout our home and on our deck, plus a sub.  Took me about an hour and a half, including 20 min on a ladder resetting speakers in our living room and was time much better spent than dealing with incompetent tech support.  System, so far seems stable at least til the next update.