Most likely things will work transparently where consumer and merchant transact in fiat, while the settlement happens in crypto in the background. The Strike app does this with Lightning BTC. As the buy and sell price are the same, it’s a non-taxable event. Both ends transact in fiat terms.
In this way, it saves a step if the consumer pays in crypto. The payment rail is already there for instant settlement. Thus, credit card issuer merely needs to convert to fiat at the merchant end.
It makes more sense with fast and cheap coins like HIVE, XRP, XLM, and Dash.