I am referring to the use of Bitcoin as a mass market currency. Physical currency is still useful in many situations where there is (a) no/intermittent networking, (b) when the cost of the purchase is less than the financial overheads and (c) for truly anonymous purchases.

I could keep going. There is a reason that even in countries like Australia where we have widspread tap to pay that cash is still pervasive.

There's no reason bitcoin can't coexist with physical currency. An interesting question is if bitcoin were accepted everywhere, what would people trust more? Bitcoin or bits of paper printed by the government?

Go to China. I do not carry cash at all.