Since the new devices came out, I tend prefer the sound of some of the older devices.

The Playbar SOUNDS better that the Arc, but the Arc adds more depth to the room.

The ZP100 SOUNDS better that the Connect amp and the Amp gen 2. But the latter has more power.

That being said, The Era 300 would be the the best update for the Play 3.

But… Have you tried to update the Play 3 to the S2 app to keep it as a part of your system?

https://support.sonos.com/en-us/article/sonos-app-version-compatibility

I have a Play:3 in my study running S2 it is great for music.

If I was replacing/updating it I would probably go for an Era 100, I have a pair as surrounds and the music quality from them is really good. 

Thanks for both yr advice!   (This a great user community!)   Mike 

If you want too move the Play:3 to S2 probably best to do it from a PC or a Mac as the App is still unreliable for this type of task as far as I can tell from the posts here. 

A Play:3 is not S1 only, you can use it on an S2 system.

Thanks.   I think I’ll therefore upgrade my two v. old 2010 Zoneplayer S5’s (obligate S1 app only) to current ‘Five’ speakers (S2 app only).  Then I can run S2 app without having to have two apps and two separate systems.  Thx for advice/help. Mike