Well, I think that there will be higher acceptable if there is a service to fit the gap by collecting Bitcoin from the user and paying fiat to the merchant. There won’t be any risk to the merchant in this case.
There already exist a lot of services like that where merchants can accept bitcoin as a payment method method. Some of the best ones are Bitapy, Stripe or Authorize. They already have thousands of merchants all around the world accepting bitcoin but the problem is
most merchants accepting bitcoin are working only onlineI'm not sure how you suppose to use cryptocurrencies offline
Other than that, you can still use Bitcoin payment cards in pretty much the same way as regular bank cards if this is what you meant. If you actually mean using cryptocurrencies in the same way as cash (i.e. coins and banknotes), I don't think it is possible unless we are to use "paper" coins (for example, bitnotes). However, it will likely be against the whole idea behind crypto (though things may change with LN expansion and universal adoption)