"It" is the recall or confiscation of cash, i.e., dollars, euros, pounds, etc., in physical form. And a key justification that those calling for this radical measure cite is that it reinforces the ability of central banks to impose negative interest rates.

Negative rates mean that lenders literally pay businesses and consumers to borrow money. They also penalize savers for hoarding it. The Danish and Swiss national banks have gone the farthest into negative territory, with interest rates of -0.75%. That means €100,000 in a euro-denominated account in Switzerland would be worth only €99,250 after one year. While these rates apply only to "excess reserves" banks maintain at the central bank, nothing stops banks from requiring depositors to share the pain.

But that's not enough, according to some economists. Citicorp's chief economist, a technocrat named Willem Buiter, thinks the US needs much lower interest rates to push the economy out of the doldrums. He thinks negative interest rates around -6% would do the job. But there's one condition: For his plan to work, he says, the government must abolish cash.