Probably bitcoin will never replace dollar, IMO at most it will become widely used, similar to euro in Europe.
Sometime i also think that bitcoin will never replace dollar because bitcoin just a crypto currency and there is no physical shape of bitcoin and Dollar have physical shape and Dollar is accept in everywhere for online and for direct shopping and currency we can buy every think from online with bitcoin nowadays .
You are right with what you see, it can never happen, bitcoin cannot replace dollar soon and in the near future. It will still be an alternative currency without a value if without fiat, so basically it relies on fiat.