It depends on how a country will accept bitcoins. Because they are also using their existing currencies, but there's not much difference in it, both are useful in their own ways, they also have their own limitations,bitcoins are essential whether it is used in the form of investment or currency.
As we all know bitcoins can be used both it either as bitcoin investment or a currencies and if you want investment it is more than any money in the world how fast it grows can you imagine if you just hold for several years how much you earn. And if you also use it for currency for as we know it has been no boundaries you can use it every where around the globe economically.