I have a different opinion from you
In my opinion, Bitcoin will not become a global currency in the future, this is a currency that proves the existence of Blockchain technology and is a payment instruments for the project which base on Blockchain technology.
I think if we have to have a Cryptocurrency in the world which is used to pay for normal transactions, that is not Bitcoin, it's a other Cryptocurrency that is based on the Blockchain technology is developed in the future. In order for a Bitcoin to become a currency that the value of it can not be so variable continuity.
So, I do not think Bitcoin will become a normal trading currency but it will help the later Blockchain platforms grow.