Well it is possible (and very likely) that cryptocurrencies will displace fiat currencies in the next 10-20 years. Since neutral control, freedom and decentralization are at the centre of cryptocurrencies, it means that whatever currency it will be, it will be massively spread worldwide and every person will have their "personal wallet" possibly in a form of a wristband or headband, or if the RFID will become more popular then it will be in a form of underskin chips. I don't know how it all will be controlled but I think there will be some sort of illusion of "freedom". You can buy and sell with your "personal wallet". Since Satan's most powerful weapon is deception, very few will be aware of what's really going on. Who knows, maybe this process is aready started. And the mark of the beast probably won't be as obvious as 666 but it will be some other numerical sequence like 3x37x6  or another sequence that makes up 666.

My two pence