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.
Bitcoin is not a real currency it is the virtual one. It is created by digitally and use by digitally. In my opinion it a currency because it doing all those things which are done with the help of real currency but in digital way. Many online merchants and business using Bitcoin as trading tool. They taking Bitcoin instead of real money from their customers. Bitcoin is also use to pay monthly rents, EMIs, water and electricity bills etc. Bitcoin is also convert to any country currency like a real currency. And like this there are some other uses of Bitcoin is present which are comparable to real money 