In their push to dethrone the U.S. dollar as the world’s largest reserve currency, the BRICS nations—or Brazil, Russia, India, China, and South Africa—have been talking up the idea of a common currency for years. But Jim O’Neill, the veteran economist who coined the term BRIC (the group did not originally include South Africa) when he worked at Goldman Sachs in 2001, blasted the plan this week.