From what I've read, for the vast majority of merchants, crypto is something that they didn't learn to trust, plus according to Kris Marszalek, CEO, Crypto.com, "Crypro's price swings is not really conducive to merchant adoption."
However, nothing is impossible right? Who knows that in the future, merchants around the world would learn to take risks and adapt crypto payments. Or maybe crypto may even have stable price. We don't really know. It's just that, for now, crypto cannot replace fiat.
Agree. Crypto's biggest issue is volatility. Unstable prices on the market makes it more suitable as a store of value than digital cash. It's no wonder why serious merchants and businesses alike have accepted Fiat on top of crypto. Losses or gains can be reflected in a blink of an eye due to the uncertain nature of crypto. I believe that stablecoins are a more suitable replacement of Fiat, although some of them are linked to real USD reserves. Depending on the blockchain network they're based on, their fees could be extremely high or dirt cheap. Speed is also an important factor to consider here. Since Fiat is instant, stable, and reliable, it'll be actively used in the mainstream world for a very long time.
Nonetheless, no one knows what will happen in the future. With a friendly regulatory environment for the crypto/Blockchain industry, we could see the "impossible" someday. I'd expect Bitcoin and other major cryptocurrencies to have a stable price relative to Fiat to serve as a viable alternative to the world's monetary system. Only then, people will be able to use crypto more thoroughly as they would with Fiat. Considering that both ends are distinct from one another (either centralized or decentralized), it looks likely that they'll survive for a very long time. People will have a choice between crypto or Fiat for mainstream payments. The diversity of assets is what makes our world a better place. There's really isn't a dominant form of money, since each asset has its respective value/use cases in the mainstream world. Hence, neither crypto will replace Fiat or vice-versa. Just my opinion