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.
It has a point. A fiat is called currency because it is inskde the market, or it is what helps the economy to run. But if we see through those products we can comprehend that bitcoin also performs this kind of things. With this we can say that bitcoin is a currency, eventhough it is used as an investment.