I see it's for small parcels, kind of Takkyubin style I guess. So trains aren't good for that.

The article says the 23 billion cost would be for a 300 mile tunnel, which in my opinion makes no sense whatsoever. Such a tunnel is impossible to make, and if it were possible it'd cost orders of magnitude more than $23 B. But I could see a tube or similar device running parallel to the shinkansen and radial last mile delivery by truck/hand from the stations along the way.

Anyway I think that Japan's social specificity makes it the perfect place to deploy driverless trucks and that's what will happen in the end.