How often do you have power losses, to need this as a feature? 
 

Can’t you just set up the group(s) you want and save them? Sure, it’s a workaround but to push the button to select your group doesn’t take long.
 

And I think the development team have a few more urgent issues to address before getting anywhere near this on the “to do” list. 

Since you don’t want to hear “by design” quit reading at this point.

For anyone else, the Grouping data would need to be stored in the non-volatile internal memory in each Sonos device. It could be done but it would be a non-trivial change. With the saved Groups option the original low demand for this is likely now even lower and it isn’t likely to happen.

Sadly that justification applies to several features I’ve asked for in the past, I’m not even hoping at this point as the Sonos position makes good sense even if it doesn’t satisfy my desires.

of course… you’right… think at the morning, when the alarm has to wake you up and nothing happens… and you arrive late to an important meeting or something like that… or if you’re sleepy and have to switch on your pc and reset all the groups… nothing? this is a correct ‘design’ in your mind?

what I mean is that In more than 9 years hasn't it been possible to set up groups in a non-volatile? and In addition, you have also removed the alarm functions in the iPad app ... very easy to say “...quit reading at this point. “. This is how the customers are treated

The non-volatile memory (flash memory) used by Sonos has limited write cycles; that is, there is a limited number of writes before the material starts to break down.  Once a sector has deteriorated, it is marked as unusable, causing an ever decreasing storage capacity*, and eventually breaking down entirely.  There is typically around 100,000 write/erase cycles until the circuit begins to deteriorate.  For this reason, the writes are kept to a minimum, and writing out every group/ungroup would be impractical, given grouping/ungrouping is a core functionality of the Sonos system. 

It is also very slow to write to, which could cause a performance hit.  But this is secondary to the write/erase limit.

*One can see this deterioration at work with the problems seen in the Connect/Connect:Amp units that appear to be having storage issues in this thread:

How would you decide whether a speaker has been switched off, a circuit breaker tripped or a power cut occurred?

From a speaker perspective it looks the same. If someone unplugs a speaker for a few days because they’re moving/taking it on holiday, doing building work, redecorating, should that speaker try and reform the group it was previously in when it is switched back on?
What if the speakers around it have been grouped differently since then?

When a breaker in the consumer unit trips, I sometimes need to switch things off on the circuit before resetting it, then switch them back on individually to either prevent the breaker tripping immediately or to try and identify which electrical item tripped it. Depending when it trips I might not bother switching everything back on until I need it.

How long should an unseen speaker be kept in a group for? 30 s, 1 hr, 1 day, 1 week, 1 month.
What if it has actually died or been sold and is never coming back?
Should the other speakers keep looking for it when they come back online or remove it from their group?

I am curious about your alarm scenario. You set an alarm against a group you have setup rather than on the individual speakers? What happens to the alarm when you change your groups?

I’ve never needed to use the Sonos alarm function so have no idea how it works. I have external automation which runs wake-up/sleep routines which worked directly against the individual speakers at different times rather than groups.

There is a potential, that the last known group information could be retrieved from the Sonos Cloud Platform when a speaker starts up depending how long Sonos keep the information when a speaker goes offline.

External controllers can use the cloud api to retrieve group information, but whether the 30s timeout since last seen is just how it is presented to subscribers or whether it is also ungrouped in the cloud platform is anyones guess.

https://docs.sonos.com/docs/subscribe#tag/playback/operation/Playback-LoadContent-GroupId