How can it be?
Why would any country accept a totally global digital currency as legal tender in their country?
A currency with open source coding and not controlled by anyone,
A currency which can be forked by anyone at any time.
The answer my friend is no.
Why are you saying that. Bitcoin as already accepted as legal tender in Japan, and Venezuela is already doing the same right now. We also have some states that are trying to allow it's citizens to pay their taxes with bitcoin, although I think it will still be seen as property there, but I'm not sure about that one. It all depends on how regulation gets done, but it will perfectly normal for that to happen in the future. I don't see bitcoin replacing fiat, but being accepted as legal tender is possible, and it is already happening.