Who says that bitcoin's intention is to replace fiat? It was design as a payment scheme by Satoshi, its just in the last 10 years bitcoin has evolved and there are proponents that it could be future's single world currency. But I doubt that, fiat has still its place in the financial industry no matter how you look at it. Currently, we can co-exist with the fiat system, so no one is replacing some one here, nor making it obsolete in the next 50 years or so.