It might be under current laws. Obviously it's never been tested for cryptocurrency, but for example, gold coins are explicitly declarable. Here's
one opinion:
Travelers entering the United States at the border are already obligated to declare any currency holdings of $10,000 or more, regardless of whether or not custom officials might have the means to detect those holdings. While digital currencies occupy a somewhat unusual place in many portions of finance law, a report by Smaulgld suggests that the situation is relatively clear in this case. Because digital currencies technically accompany a holder anywhere that he or she goes, including across a border, that traveler would need to declare his or her entire cryptocurrency portfolio every time he or she enters the United States. This is different from the requirements of travelers who hold bank accounts and/or precious metals valued at more than $10,000 which are stored outside of the country.
Indeed, some US senators have been trying for the last couple legislative sessions to explicitly have digital currencies included (among other things):
The proposed bill, designated U.S. Bill S.1241, was introduced on May 25 of this year and co-sponsored by Sen. Diane Feinstein (D-CA), Sen. John Cornyn (R-TX), and Sen. Sheldon Whitehouse (D-RI). The bipartisan group of Senators who have put the bill forward hope that it will deter individuals entering the United States from bringing in undetected and undeclared assets in the form of digital currencies such as Bitcoin and Ethereum.
In either the US or NZ, it seems most of us agree. The easiest course is to delete any cryptocurrency wallets and restore from seed later.
