I somehow believe that bitcoins will rule the world but I guess it won't torally be used worldwide since not all countries have access to good internet. Many third world countries suffer from these incoherent internet connection. Plus, fiat money is as powerful as bitcoins. Bitcoin will be the world's digital currency but I think not as a daily money.
bitcoin will rule the online world maybe but i think not on a real world because bitcoin is purely digital and will only work mostly in an online environment and without internet connection i dont think we can use it to buy stuff's offline not unless they can invent an offline version of the blockchain or if someone can invent a physical coin and embed the private keys and wallet address on it. but overall fiat money is still powerful and will never be replace by something digital.