Sonos does not do the implementation, they only supply the API. It’s up to Apple what features they wish to implement using that API (which obviously supports Hi-Res because other providers use it).
You might be interested in knowing that the head of Apple Music Services went on record to say that no one in Apple engineering can hear any difference between Apple Lossy AAC and Apple Lossless, once sound levels are matched. You are better served spending your energy elsewhere, and time on enjoying what you get even now from Sonos/Apple Music.
My 2 cents.
PS: Ignore all this, I see we have had much the same conversation 8 months ago.