Problem is your parents or anyone else in the mainstream still won't use it. There is no denomination and they won't have any confidence that it won't be hacked. There is a reason that physical assets in private vaults are fiat and precious metals... their value is self-evident with the printed or forged denomination and therefore these assets are completely trusted and fungible by everyone. Once you cloak the value in a card behind proprietary tech, all bets are off for mainstream adoption.
Problem is your parents or anyone else in the mainstream still won't use it. There is no denomination and they don't know that it won't be hacked. There is a reason that physical assets in private vaults are fiat and precious metals... their value is self-evident and therefore completely trusted and fungible by everyone. Once you cloak the value in a card, all bets are off for mainstream adoption.
This is interesting, though ultimately the private key is ostensibly only protected by a pin code of a few digits. At the end of the day that might be ok since no one would reasonably carry a large amount of cash in their wallet. Perhaps one would only load small amounts to their corresponding BTC wallet for the card.