Slippery slope can be argumental if you provide the actual argumental reasoning for it as I was thought it could be used as deductive argumentation (though that does not say much). On itself it is a fallacy.
I don't see how verifiable credentials with zero knowledge proofs provide that however.
The Party doesn't care about the Proles, only the members of the Outer Party.
I think that it's rather funny that people like to appeal to 1984 as if the only point of Mr. Orwell was that surveillance is bad, missing the entire point about stuff like the control of the language or the idea that the only self-justification of the (Inner) Party is power for the sake of power (see also: The Theory and Practice of Oligarchical Collectivism).
I'd even go as far as to say that if "telescreens are horrible" is the only thing that someone takes away from 1984, they've frankly missed the point.
This is the next two steps into 1984.
Once you start mandating this, there's no going back.
The next generation will start associating wrongthink with government IDs. (Wait, we already do that, right?)