Is that a render of what they're planning? That mic button doesn't look like a switch. It looks like a momentary button. I'd want something that has two distinct positions to confirm it is physically disconnecting some wire, as opposed to a button that may control an electronic relay.
The trouble is hardware. I use rpi 0's to 3's with snapclient installed, and an audio hat, either a quality DAC or an Amp. This then feeds your amp or speaker.
I run snapserver on my computer in the common area, and it has Spotify, as well as any other audio source (YouTube, mp3's, streaming radio, etc).
I like it, I even built a portable speaker that takes a ryobi power tool 18v battery
There is a delay between the server and the sound, but all clients are synced.
It is a bit of a process, but the software is on github.