I think we are headed towards blockchain and crypto based coins inevitably. As globalism continues to rise, we have no other choice but to adapt a single currency monitored and regulated by everyone and none would have supreme authority over it.
The US dollar is a messed up thing. With too much risks, I would never store fiat cash under my bed because it's just too risky and will lose value. In India we had demonetization where 500 and 1000 rs notes were banned which showed me how fiat is useless concept!
The US Dollar has been the global currency for trade throughout the world for so long. So, it will take a long time for crypto to come to the mainstream. It hasn't been properly regulated yet. And many governments are against it. So, I believe that the dominance of the dollar would continue in near future too, but many governments such as China, Russia have been trying hard to reduce their dependence on the dollar.