Im thinking like an micro chip implanted in our body. This system is not out of the picture because how we discover things every year, it is not impossible that in the future this things may happen and it will boom like btc.
Its could be happen in the future we implanted microchip to our body. With technology, anybody want to be practical and if that microchip is more practical than carrying wallet, maybe many people want to implant microchip to their body because technology always involve and helping people to make life more easier