Bitcoin is still being used as currency because you can pay in millions of merchants with bitcoin and its still dominant whole cryptocurrency space.
Therefore bitcoin is both investment and currency, in next few years we will have lightening network which will make bitcoin ultimate payment gateway.
Bitcoin might keep on holding speculative value in future too but volatility might get lower down with increasing marketcap.
Agreed>>Bitcoin will most likely stabilize overtime. It will remain to be seen wether bitcoin will gain mass appeal or not the government bodies anytime soon or if another coin will win the day.