but for me it is about usage as a replacement for fiat money.
i don't see it that way. bitcoin doesn't have to replace fiat to be considered "gone mainstream". the bitcoin adoption, or the ultimate one mass adoption is when people have the option to pay with bitcoin if they choose to or continue using fiat if not.
and i have never read anywhere that Satoshi said anything about "replacing". even in the paper it is referred to as something like an alternative method.
Exactly, the key word is not to replace but to choose Bitcoin more often than fiat, debit, cc, and other form of digital currency when these options are presented when you pay for service or goods.
Replacement means eradicating the fiat completely, I don't see that happening.
I would be interested in hearing about what you perceive is the advantages of paying with bitcoin (or name your fav crypto if different)
Well, I could say "Convenience and privacy". Unlike paying with debit or cc when you like to subscribe for an online service provider or purchase a product, you don't need to link your financial information such as card number. Bitcoin could be directly sent to the merchant without linking anything.