Colombia, Scotland and the U.S. have all proposed wealth taxes in recent years, joining the likes of Switzerland, Norway and Spain in imposing taxes specifically on the super-rich. And even some of the world's wealthy are backing such calls. "This is about the wealthy contributing more to the society," Phil White, retired entrepreneur and member of the Patriotic Millionaires group, told CNBC. But can such a policy work in reality, and is it likely to take hold?