Open to abuse & certainly not privacy friendly, but in a hypothetical world where governments can be trusted on that it seems very plausible that it could be a social plus. i.e. You can probably spot trends like person X spends a huge amount of their pay on nappies and babyfood...probably could do with some additional social help. Nordic countries probably come closest to said hypothetical but still seems kinda dicey
I understand salaries are already public in Norway. Why shouldn't they be? Unless you can't justify your earnings, for some reason.
I understand the 'big brother!' response to this kind of thing, I'm also squeamish about it. It does rely on a government that is trustworthy and accountable. But I don't think secrecy, paranoia, etc, is beneficial, compared to more openness.