This seems odd to me. The "money" you have in your bank is already purely digital, a fiction. It's not as if you go to and from the bank carrying physical notes

This seems odd to me. The "money" you have in your bank is already purely digital, a fiction. It's not as if you go to and from the bank carrying physical notes and leave them in a box you control. If your government wants to take away "your" money, they clearly have the technical ability to do it by compelling the bank to freeze your assets. Likewise, that bank you are currently trusting so much could readily shave a couple of zeros off your balance. There is absolutely nothing technological stopping any of this. For the shared fiction of "ownership" of intangible assets to work, we are all at the mercy of one thing: the rule of law.