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.
I'd be interested provided it was a less permanent solution. IE, something I can actually remove/add at my own will.
I believe startups are actually already working on solutions like this. I'm sure there are many on Angel.co