I have 2 Play 1s in my system and they show as being Modern, rather than Legacy. So that I can work out how long they will be supported, does anyone know when Sonos stopped selling them? My concern is, if it was, for example, 2 years ago then Sonos could announce they’re Legacy tomorrow and so they’d only have 3 years left of support. 

They silently refreshed the Play 1 hardware in 2017. If yours are hardware version 1.20.x you should be good for years because it is (according to someone who does teardowns on YouTube) effectively same internals as the Ikea speakers. Hardware v1.8.x discontinued in 2017 so 2 more years guarantee but hopefully more.

Just my opinion, ymmv etc 

5 years from when they stop selling on their website - so probably at least 4 years as i think they stopped selling them last year.