Bitcoin is already a currency, it does not need to become one. You can buy and sell things with bitcoin and that is what a currency is for. Although now I think people use bitcoin as more of an investment than as a currency but that does not mean that bitcoin has stopped being a currency.
Most of people commonly use bitcoin as investment which they know that it will give profit. But, we want to use bitcoin as currency it need to undergo in government which they will implemented it as currency. We all know some government allow bitcoin as currency but somehow we can't say that bitcoin will really become a legal currency.