We don't need everyone to use bitcoin before it would be regarded as a currency. All we need is the multitude that would be easy to accept it for a means of payment on goods and services exchanged. You don't even need no government or regulatory body's approval. That's the beauty of the whole system as we have it now.
Bitcoin as it is and even in the future won't be readily available for all people due to certain limitations like devices and network. Those doesn't mean its not a currency. It remains a currency for those that use it for a means of exchange.