I also think that Bitcoin don't have to be a legal tender of any country to achieve it's global currency aim, if it's accepted in any country as a payment option and it's business people will adopt it and accept it as a means of payment, then it'll still mentain it's function as a legally accepted payment method. I don't think that most governments will accept Bitcoin as a legal tender because they can't control it as a result of it being decentralized, the least they can do is regulate it. Bitcoin don't have to takeover fiat currencies, it can function perfectly well as an alternative digital currency, besides people are adopting it more as as an investment asset, because it's a store of value.
Bitcoin have been popular as commodity assets for investing and trading, its difficult to make bitcoin acceptable for legal tender payment transaction because all countries have regulation by using fiat for transaction. Indeed bitcoin become more decentralized and has transparent when using for transaction, but can't control when bitcoin price dropping how many people get loss when accepting bitcoin as payment way without convert it as soon possible.
Actually bitcoin acceptable for legal tender payment transaction has advantage and disadvantage side, bitcoin increasing values could increasing profitable if accepted as payment transaction but in other side many time bitcoin transaction got congested and take more longer time payment completed.