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.
Fine, that is actually one way to put it. I guess as time goes on, this would be more like a community in the long run and those who accept and willingly use it will benefit eventually from the whole thing. Of course, it is not everyone that can simply make use of it due to some limitation reasons, or reasons best known to each individual based on their perceptions, but at the end, I do not see how bitcoin is really going to be allowed as the world currency in the case where it takes over the centralized traditional system.