You say "can't." I think you mean to say, "shouldn't." As you yourself pointed out, Powell says its unsustainable...and then keeps doing it. I'm not really sure about crypto-currency. In fact, I'm very skeptical. It's more like a share in a company than a currency. How many people spend it? Why would you spend something which might be worth twice as much tomorrow? People just buy and hold it, like a stock. The problem is that it's a stock in a company that doesn't do anything, and has no assets.
Another issue with fixing this problem is that I think people are very used to things being the way they are now, not realizing that what we have now is financed by a completely bunk method of financing. Imagine running the country the way you run your own personal finances. You earn. And you spend less than you earn, leaving some for a rainy day. It's nice, and safe. But the general public wants to see BIG GROWTH, HUGE GAIN$, MA$$IVE PROFIT$, not realizing that the reason they see that is because we've basically taken out an enormous loan. It's the difference between some guy earning $20 for an hour's work, and a guy going to a loan shark, borrowing $100, and then acting like he made $100 in 20 minutes.