It would be illegal for Sonos to do that and I can’t see that it would do much for their rep if they tried it.

IMHO it is likely that things will become worse through time for S1 users, but it’s hard to say in which way - it might affect different users in different ways.

I see no reason to continue spending on Sonos kit, as it makes sense to me to split the smart side from the hardware side. My current fall back if my hardware fails is to use Chromecast to my AV system and to dumb speakers, either via line in or to built in CC. Better alternatives may well come along, though, so AFAIC nothing’s set in stone.

For the time being I’ll just carry on using my old Sonos kit to enjoy music.

I don’t see even that happening for existing use cases. Till the hardware dies a natural death.

These are just speakers that play music, at the end of the day. Notwithstanding what Sonos/Sonos fans would like you to believe.

Depends what security issues come along, changes to radio sites and grouping sites etc, etc… It wouldn’t bother me, as pretty much all my music comes from a NAS, but it may bother other people.

Agnostic services like Spotify aim to be as widely usable as possible, so I don't see them taking actions to delete the S1 user base by their own actions and lose revenue, just as they won’t for other platforms that have been made obsolete by their makers. As far as security issues for speakers, I don't see that a major deal in the first place.

Used via line in jacks as dumb speakers, I don't see anything happen to my Sonos S1 components except hardware death - which I can accept as a reason to jettison such kit that dies.

Time will tell of course, but I am not losing any sleep over this minor issue. As some one said here recently, there is no need to let the Sonos S1/S2 actions hustle one into upgrading.