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.
Yes! Once the market gets larger (much larger) volatility should decrease significantly. The plus the lightning network will set Bitcoin up for use as a currency. Currently right now with its volatility, people view it as a speculative investment. I do think Max Keiser is correct in stating the price will stabilize at around $100,000 USD.