The queue surviving a power outage isn’t going to happen.  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 are typically around 100,000 write/erase cycles until the circuit begins to deteriorate.  For this reason, the writes are kept to a minimum (system settings, service information, new units, etc.).  If the system was writing out the queue to flash memory every time the queue is added to, deleted from, or otherwise edited it would reach the limit of the memory very quickly.  Hence why the queue is kept in RAM and not stored.

I would want to expand this a bit to have the system remember it’s last direct streaming source (streaming service or local library) when shifting to a non-direct source (TV audio, line in audio, or bluetooth).   In other words, remember what you were playing when it’s possible to know what you were playing.

That said, I think this requirement can get rather complicated when grouping gets involved.