I think what's required is electronic cash, something like a CBDC with an electronically transferable, partially anonymous system that still allows offline payments if case the central computers get knocked out. GNU Taler satisfies one half of these constraints (cashlikeness + taxability). The Swedish e-krona pilot also has a token based component to allow offline payments.
We already have this. It's called bitcoin. For offline payments, there's physical devices like opendime and potentially Chaumian mints like cashu.
When you have enormous amounts of debts denominated in a currency, so many time the price of those things that would be lost, its value is almost entirely determined on what interest rate the central bank sets. If you hoard it to get people to default so as to obtain the value of the collateral, the central bank will printing to stop you.
Meanwhile, there's no point in trying to do that kind of thing with bitcoin. The value of the collateral is probably less than the value of the physical cash. What you do then is to invent your own bitcoin and hope that somebody will accept units of it.
For this reason I believe that the fair value of Bitcoin is zero, but I can't know when it ends up at zero, so I'm not shorting it, just as I am not shorting the US real estate market, even though it's clear that from a discounted-cash-flow PoV it must be incredibly overvalued, provided that it wasn't incredibly undervalued back when interest rates were at 1%.