Rewriting the client is not sufficient. You need to convince everybody to run the new client. I don't see that happening as easily as you presume. It is highly

Rewriting the client is not sufficient. You need to convince everybody to run the new client. I don't see that happening as easily as you presume. It is highly likely that cryptobanks will come into place in the future (cryptocurrencies are not very layperson friendly right now), with traditional contractual law ensuring the cryptobanks do not suddenly change the rules under client's noses. I disagree regarding cash. You're making a blanket statement and I'm saying there are niches where cash sucks. Aside from the M-PESA example I've given, another is overseas travel. Cash can be a big waste of time - depending on your local laws, obtaining forex prior to departure can be a pain (e.g. in South Africa), the withdrawal fees are exorbitant and often unclear, the risk of theft significant, you have to be aware of local exchange rates and if you want to save money you have to be aware of the exchange rate of the cash you have on hand vs. your debit and/or credit card processor etc., then when you get back (again in South Africa at least) you have to resell your forex within 30 days, and you also have limitations on how much you can purchase in a year. Another is cash payments over a certain value -- again in South Africa, walking around with more than a certain amount of cash in your pocket is asking for trouble.