I totally believe that cryptocurrency can replace dollar in the future and there will be nobody wanna use dollar anymore 
. At the moment, there are few countries are going to legalize cryptocurrency as their local currency. Beside, as I know bank system at the moment is supporting for cryptocurrency by supporting for ICO project
This is one favorite topic I have been studying about and so far I have arrived on the conclusion that id Bitcoin is legalized by all the countries across the world, it can have a chance to become the future international currency and might even replace US dollar. But the US dollar belongs to America ant the political interest of USA in maintaining the USD the international currency is much more than the benefits they might get if Bitcoin become one. So I do not think that will happen.. At the moment, there are few countries are going to legalize cryptocurrency as their local currency. Beside, as I know bank system at the moment is supporting for cryptocurrency by supporting for ICO project