undoing updates

Beware: going back to S1 did not work for me with a One recently, and I tried everything. YMMV.

The important bit (at least, at this moment in time) is that to actually downgrade a ‘compatible’ Sonos device to S1, you must first have an ‘existing’ S1 Household already setup & running to add the device to, for it to then be forcibly downgraded.
 

Without an existing S1 Household, you would either need an S1-only ‘old’ Sonos device to create such a Household to start with, otherwise (quite possibly) you may (just ‘may’) require the help of Sonos Customer Care to ‘perhaps’ resolve the matter… I’m not sure about the latter option however, as I have not heard of anyone going via that route at the moment.
 

I think many will just probably stick with their S2 setup ...er...once ‘the bridge’ has been crossed.

Like I said, this did not work for me. I had a Symphonisk on S1 and could not take a One back to S1 after having upgraded it (elsewhere) to S2. There is a thread somewhere on my travails.

Strange controlav, I can’t say that I have a symfonisk device to test that particular scenario, but I have certainly (and recently) upgraded and downgraded several Play:1 speakers here, but my existing S1 HH consists of a Bridge and at least one Play:1 Speaker that I chose to keep separate on S1 to my main S2 Household. 

I do expect the Sonos policy to perhaps change on downgrading eventually, but there has to be a route for those users who which to sell S1/S2 compatible, but upgraded, devices onto those users who only have an S1 Household - at least for a certain period of time.

You’d need to temporarily remove the S2 app from your mobile device, apparantly it’s messing with the downgrade process.