I don’t see Bitcoin completely replacing fiat anytime soon. Governments will always push to keep their own currencies in play, and most people still trust what they’ve been using all their lives.
But Bitcoin has its place, it’s borderless, inflation resistant, and can be a lifeline in unstable economies. I think the future will be both side by side: fiat for everyday spending, Bitcoin for savings and big transfers.
I don't see Bitcoin replacing fiat currencies no time soon, it'll never happen, even in countries where it's supposedly legal tender, such as El Salvador. Bitcoin's purpose was never to replace fiat currencies, but to co-exist. This topic has been widely discussed on the forum, Bitcoin in its current form, isn't convenient to be used for daily usage. I highly doubt this is going to change anytime soon.