The future Bitcoin price will be increaseing because next few years there are many countries allow to use BTC and adopt the cryptocurrency for earn money . That time is not so far where money and Bitcoin use as same world currency value . Someone can tell my thoughts are over ambitious but when it will happen then believe .
I agree on your prediction that bitcoin and fiat will be available soon as both currencies in the future because they are made to co exist and not to create competition in the field of financial system. But certainly, the process for bitcoin to be a currency is very tough knowing the government as of now is still very pessimistic about legalizing bitcoin and accept it as a currency.
However, talking about the future price of bitcoin will always be uncertain. Its price will always create changes so if today its very bullish, then tomorrow the price might be dumping suddenly. It just means that bitcoin has still no definite price even if we always say that its price will always go skyrocket as years go by. It will always have chances to dump and leave its value at a low price but not literally zero value because as long as the demand continues, its price will never be zero.