[CryptoGhost]

>perhaps some day one will replace the USD

USD is fiat currency. Fiat simply means by decree. USD is a currency by decree of the US Govt.

It's highly unlikely Bitcoin would ever become a fiat currency by the US Govt. It's also highly unlikely the US Govt would allow a free banking system and allow a cryptocurrency like Bitcoin to fill the void naturally.

Also, Bitcoin can evolve overtime through consensus of it's users. So it is highly unlikely it would be surpassed by a cryptocurrency that is like Bitcoin but marginally different, it would have to be something radically different.