Yes I think that bitcoin will replace FIAT all over the world, but it's code should be improved again and again.
But I don't think It will replace FIAT,Never.Only bitcoin adopters in their world they would see BTC replace the FIAT not knowing that the world is not just what they see and believe to be.It's vast and it's not even possible for BTC to replace 10% of worlds FIAT
I agree that bitcoin will likely never end up outright replacing fiat, but I think it could certainly supplement it.
I would not discount it replacing most fiat based transactions that occur over the internet, especially with "trusted" sellers.