It doesn't cost any more to store bits or paper in Europe now than it did when interest rates were positive. The "storage costs" metaphor as a justification for negative interest rates is a whopping falsehood.
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They could just abolish cash (suggested some years ago by Willem Buiter at Citi). Rogoff at Harvard is a proponent of abolishing high-denomination bills.
"Just" abolish physical bearer money, the the main form of money for millennia until recent decades, leaving us only with digital accounts centralized under banker control. Spendable crypto or gold would also foil their ability to extract haircuts, excuse me "negative interest".
