Firstly Bitcoin wasn't created to replace traditional currencies it was created as an alternative currency, something different from what we're used to. I don't think that traditional currencies can be eliminated because they're the identities of countries, except if the whole world becomes one global economy. That is where Bitcoin can be considered as a unified global currency but I doubt that something like that can happen. Again Bitcoin wasn't created to make any economy better, it is a store of value for anybody, institutions or government that holds it. It's a decentralized digital currency for those that enjoys their privacy, those that are avoiding fiat inflation and those that wants to make profit because it is a valued asset.
You made a good point here and again Bitcoin was not also created to combat with any other currency or our fiat and beside both curency has their purposes and functions, of course you're right, traditional currencies can not face out completely because even as adoption is taking place globally, we still have some individuals that don't and won't believe in Bitcoin no matter what you tell them, another thing is the government, government of many countries differs in decision making and I don't think any of this nations will want to face out their traditional currency to replace it Bitcoin that has not been made handy beside Bitcoin is a digital currency, an asset, an investment and means of transaction, Bitcoin was created to give individuals hope especially those that are fade up with financial institutions and want to seek for alternatives way to add value to their money.