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.
Let's settle those countries if they will impose ban or not whether they ban it today, they can just lift it up when the big countries starts to use bitcoin as an alternative payment system worldwide.
Like what I've said that there's a long way before it will happen and there's a lot of things that can change on this matter.