Spitballing here: Could there be a way to set up some quasi-legal certification service that augments rather than replaces the existing system?
Two things to note though: the Japanese registry system was originally set up so the government could keep track of its people, and given the level of anti-government paranoia in the US, I highly doubt that sort of change would get support.
A majority of Americans don't even support a uniform ID card for all citizens, which almost every other country has.
> The national koseki system thus started as part-demographic information collection system, part-surveillance apparatus.
> The current Japanese preoccupation with privacy may thus reflect recent historical experience of not actually having any.
It doesn't even need to be on federal level. Just think about it - koseki was designed mid-19 century and used paper records held by municipality. Churches in Europe kept paper books noting marriages, births and deaths even before that.
The downsides are obvious:
- in case of need you should go to same municipality and get extract from same book where event was recorded; - you only can make record in book of municipality where you are resident.