I don't think it will be any other fiat currency that will gradually replace the US dollar as the #1 reserve currency. I'm thinking more along the lines of crypto and legacy financial systems merging and the role of Bitcoin becoming more predominant. All of this will be very gradual. There will be no collapse. Why? As you pointed out, it will not be easy to unentangle any large currency from the global financial system if it is the currency used a very large number of outstanding long-term contracts.

What I'm looking at is the very long-term future. The sheer potential economic mass of the currently underdeveloped regions of the world is so large that they will eclipse the current developed word. Look at India, for example. It will soon surpass China as having the largest population of all countries. There are many, many low hanging fruits to be picked in India. There are countries like Vietnam that has already seen a lot of development but also its neighbors like Laos or Cambodia whose economies are at a very low level of development. The government in Cambodia is pretty terrible in terms of corruption. But, increasingly, the population are getting access to means of educating themselves as the cost of computing, bandwidth and memory keep falling exponentially. Young Africans are increasingly tech and internet savvy. There are many of them on Hive. These people are the future. Africa has massive upside potential.