Our currency is also unstable just like bitcoin, the only difference is, it doesn't undergo the same rise and fall as Bitcoin does. If money is an asset, bitcoin is an asset, then why not consider bitcoin as money? Simple logic. Everything that has a value money in their different way.
Even when bitcoin's price is $ 0.1 is still considered as money. However, it's not ready for payment method as we can see the fees are too high and it takes a long time for a transaction to get confirmed unless you pay a higher fee.
It's true that bitcoin is a speculative asset where there is no fixed value, frequent movement of price can be expected. However I don't believe it's ending soon. It can still stand for a long time, and can be consider for long term investment that in anytime can be converted into money.
I might say that it's a speculative asset, but we can't deny that it's also money or currency. The point is when people still use it for transaction or purchase anything it'll be mentioned as money, you know what the reason why my government couldn't ban bitcoin where transaction using other than our official currency is against the rules? Yes, because of the speculative asset, everyone has their own right to holding something precious like bitcoin.