Bitcoin won't ever become a world currency. Go look at places below or at the poverty line. They can't afford to own a Bitcoin wallet or have access to one.
I beg (no pun intended) to differ, even in places like kenya people like poor farmers are doing bitcoin transactions using SMS services on old (non-smart) 2g phones! ( CoinPip ) And yes ok, not all the world has a phone, but that too is changing very fast.
There are more people with a cellphone connected with the internet than there are people who have a bank account.
Banking is ridicously expensive compared to owning an internet phone, especially for poor people. Bitcoin is much more accesable to the poor than banking is. And that's one of the reasons it will catch on.
The poor might even come out ahead of the slackers who still believe in fiat, just because it works for them now. By the time they realize the fiat system is failing they will be poor in bitcoin terms, and their fiat will be quite worthless.