Thanks.
Just took a look at Naim Mu-so. Looks good, although seems to be a much higher price bracket than Sonos. I can't see any wireless speakers in Lyngdorf range. If they need to be wired to an external amp or AV receiver I'd consider that a different type of system. Looking at current Denon wireless speakers (Denon Home range), I don't see mention of chromecast built-in.
Regarding adding Chromecast via the old chromecast audio streamers - yeah they can be achieved with Sonos too. But in your original comment I thought you meant you only get devices with Chromecast built-in. Getting entirely wireless speakers which support all of Airplay, Chromecast built-in, and UnPnP, is what seems difficult to me, especially in the Sonos price range ($150 - $450). Chromecast built-in often seems to be left out.
I didn't want to make this about Chromecast, but about not being locked into AirPlay. We don't have that many wireless speakers, just regular AV Receiver - speaker combos, sometimes with some amps or power amps in between.
Off the top of my head, the Naim (smart speaker) and the Lyngdorf (integrated amp) do native Chromecast. I have two audio pucks and I use only one, it's plugged into an Electrocompaniet (also integrated amp), so my wife can Spotify directly into it (she has a Pixel phone).
The Denons are AV receivers, one is a 8500HA and the other is a 4700H. They don't have Chromecast but they're fairly open in terms of streaming capability, uPnP, AirPlay, Spotify included.
But otherwise we're as multi-platform as we can. Of course it's not always possible or feasible to get stuff that supports everything.
In any case, being locked into AirPlay is a terrible idea from where I'm sitting.