Weird ice cream flavours have in recent years spread like wildfire and now include such inviting types as human breast milk, raw horseflesh or sardines and brandy. Is something similar happening in the world of ETFs?

Mario Draghi, chairman of the European Financial Stability Board, hinted as much. On Monday, the FSB delivered a more detailed report on the matter, noting that these once "plain vanilla" investment products have taken a "disquieting" turn and have tacked on, "new elements of complexity and opacity."