When will currency/coin become a rarity?
Response to comment [from a Christian]: "How much longer before cash becomes a rarity, a thing we rarely see..."
We are certainly headed toward a cashless society. 
"Antichrist’s mark will allow people to engage in daily commerce, including the purchase of food and other necessities. Without the identifying mark, individuals will be cut off from the necessities of life..." MacArthur, John Jr: The MacArthur Study Bible. electronic ed. Nashville : Word Pub., 1997, c1997, S. Re 13:17
