Forget Bitcoin, think IMFcoin. The head of the International Monetary Fund has been musing about the future of money, and thinks there is a decent chance it will come from the guardian of the world’s monetary system.

Christine Lagarde, IMF managing director, held up the organization’s special drawing rights (SDRs) as having a possible digital future at a Bank of England forum last week, and put what she said was a “question mark” over whether SDRs could replace existing international currencies. “It’s not a far-fetched hypothetical,”...