So my question is can bitcoin be a main currency of world economy?
It will become the main currency for crypto economy but not for world economy.
There's a long debate on how will bitcoin going to overtake the currency worldwide but there's a long way to go before it will go there. Dollar will stay and bitcoin will be it's rival and alternative choice for people who wants to stay anonymous.
It is also depending the legality of bitcoin of that certain country. Some stated that it couldn't happen that it become a world currency due to current currency of every country which economy rely on it.
Irrespective of the legality which is something that would be in place in the long run anyway with governments all over the world coming with their own regulations one way or the other but we cannot expect the government of each country to start adapting bitcoin fully as a currency in replacement of their own centralized form of currency or simply put government replacing centralization with decentralization, I don't see this happening in anyway.
Bitcoin is all set to impact the economy of every country. Because when more people from one country start adopting it, it will give consequences in fiat circulation as people may start exchanging bitcoins within them for goods and services. Future of any country's economy will be decided by bitcoin for sure.