This is a new behaviour, and I really don't like it. I *never* sign in, and I already hate all the nag screens that try to force me to. I don't care about (or want) the "extra features".
But since Sonos started this business of progressively disabling aspects of the system to force me to apply updates (which is evil in and of itself), I think it's grossly evil to force me to sign in to even get the updates.
There was no "sign in" when I bought the system, and unless Sonos is prepared to reimburse me for the cost of all the components, it should continue to operate (at least at the base level it had when I bought it) without needing to sign in.
I have long stopped buying anything new from Sonos because of this behaviour, and I discourage friends from buying it either, because of this whole "forced sign in" business.