I think BTC can replace fiat sometime in the future, with how technology develops it's pretty possible to see BTC at such a level sometime later.
Stop with dreaming. Bitcoin is an alternative, how hard is this to understand? Fiat currencies will remain as main currency in the world. Bitcoin can't change that.
Possiblities there dude. If you take some long years the world belongs to Barter system Only After that Some of Asian, Greek and Roman Kings started Coin and currency system. As like bitcoin also possible in future Digital world. Adaption and many users day by day in Bitcoin forum is example for that.