Sonos has stated that as a minimum, they will support speakers on the current software version for five years after they stopped being sold/manufactured by Sonos. They will continue to support legacy speakers using the legacy software as long as possible.

PLAY:1s are not legacy speakers. While they are no longer manufactured or sold by Sonos, they do operate on the S2 software.

Unless you need a speaker that has a built in microphone, I see no reason to upgrade them. I have six of them, and zero plans of upgrading them at all. 
 

Agreed.  I was tempted to use the 15% upgrade offer to replace play:1s, but I will wait until a speaker fails or there is a new feature I like isn’t available on the play:1.  Since my play:1s are only doing surround sound duty, that’s unlikely to happen anytime soon.

Thank you all for your response.

Moderator edit: removed spam links from quote.

It is SPAM, guys.