I can imagine how digital currency would work when it comes to myself as my employer does direct deposit so I would be forced to do all transactions with credit cards, check, or debit. I assume the Fed and banks would just stop distributing cash and that would dry up. I don't even know if they would outlaw cash. If I wanted to sell a gun, would I just have to use a Paypal app or some other service?
What gets tougher is all the people who don't have bank accounts. The not so small number of people who take their paycheck to a check cashing place every week would have find some other way to spend the money. Would they use an online app and just transfer money? For the people who don't do tax returns, that gets complicated.