So my question is can bitcoin be a main currency of world economy?
Bitcoin can be the world's currency without government support. Bitcoin is easy to use, and getting bitcoin does not need to go through the government, so you can use what you want. If you want to buy an item then using bitcoin you can buy it in a country that accepts payments using bitcoin. Bitcoin being the world's currency has been achieved now, many people or maybe in all countries in this world there will be someone who uses bitcoin. Bitcoin is not centralized so there is no need for the government to use it.