Things have happened since the equation of exchange was developed and they increase current aggregate demand and run the risk on decreases AD in the future.
1) Nixon took us completely off gold in early 70's. Money supply can change up or down without printing so we will never need wheel barrows.
3) Federal debt, once only used to finance war once they had begun now finances social programs and 2.5 wars that might happen.
3) States and companies promise retirement they may not easily finance in the future.
Question! How many econometric models incorporate these concepts?