I find this hard to understand. The dollar has always been far more secure as a currency than the Peso. And every Mexican vendor I ever met would take dollars.
I hope they have not passed laws to make it impossible for vendors to exchange dollars, because if not they will just ignore the government.
It could be an excellent tool for to fight the drug trade, though. Can you see a coke dealer asking his bank to exchange $250,000 in new $20s into 2,000,000 pesos?
What are all the illegals going to send to their families in Mexico now?