i think cryptocurrency will become the official payment system in the world. but i can not exactly which coin will be the official tool, BTC, ETH, IOTA or XRP,... no one can know.
Yes it is right that digital currency/cryptocurrency will be the future of the world economy. But I am going to clear your doubt that it will be the Bitcoin which will be that coin. You can see that all of the governments who are taking interest in the regulation of crypto are giving more attention to Bitcoin which means that they are seeing something special in this currency and it is sure from their action that they are making this currency a more trusted currency for the bigger companies of their countries and for the involvement of investors.