Unconventional tools deployed by central bankers from Frankfurt to Washington to mitigate the economic fallout of the financial crisis may be conventional when the time comes to combat the next downturn.

The Federal Open Market Committee (FOMC) is already discussing the issue while other central bankers and economists in developed nations debate whether to holster emergency policies—bond buying, targeted credit programs, and negative interest rates—or make them part of their everyday armories.

The shift beyond a short-term interest rate as the main lever of monetary policy could force investors, consumers, and businesses to make sense of a world with multifaceted, sometimes arcane policies. Toolkits expanded since the crisis seven years ago are encountering resistance from lawmakers and others who argue central bankers have gone beyond their mandates.