This is the product of self-righteous activism. You'd have to be pretty deluded and starving for attention to think effectively releasing tens of millions
of private individuals' complete identification data is justifiable in some way.
If they, on the other hand, get thousands of customers complaining and leaving, they'll take security much more seriously in the future. There's also a good chance that affected users will be more careful and proactive about their personal data in the future.
In the immediate, the only thing that can happen, if at all, is for some people to lose their jobs.
I think he is hoping that if the leak is well covered enough by the media, it will be adding oil to the fire of public discontent. Perhaps in a way that would dislodge the current government.
Way I see it though, that's quite a long shot :)
Whoeves did this is an utter idiot, a profoundly inconsiderate hacktivist, whatever that shall be.
If this data was so easy to get, any state actor probably had it for years now. Also powerful criminal organisations.
Wasn't the harm potentially done already and this might trigger a change? Maybe now all those banks will not accept whatever data is in this leak as a way to authenticate a customer. In that scenario we would be in a better situation because of the leak.