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.