What happens when they bust out the $5 wrench?
To be maximally effective you'd need to mobilize enough attackers and enough windowless white vans to reach the entire populace within probably a day, so let's say 3 million attackers and 3 million white vans. That's when things start getting more expensive than the sql query.
i would guess that percentage of people with wallets would be very small and a relative small team could with a relative small number of white vans and wrenches could get every single one in relative short time..
and for countries that heavily monitor internet usage, like china, i bet they could have a list with pretty good assumptions on who has crypto that they can target for further investigation before sending the wrenched goons..