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.
This is not true and if you read this forum and / or news you would know it. Even in most undeveloped countries, ppl use OLD mobile phones that can send sms messages, and to use Bitcoin, SMS is all you need. Little bit of electricity, and connectivity and BTC can go to any place where Banks can go. Places that have absolutely zero electricity and connectivity to rest of the world AND are inhabitated arn't really in large percentage.
And there are movements (google) that are working on tech that would enable wifi access to any place in the world. All someone needs is little bit of electricity (one single small solar panel) and low poerd device like old phone, and there you go...BTC access.