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Bitcoin I think was created to be used as a currency and a currency means something which could be used as a means of settlement. So if you want to say that Bitcoin was not created with an intent to replace dollars then you are really mistaken.
Just because Bitcoin can be used as a currency doesn't mean it has to be used as a national currency. Fiat and Bitcoin have vastly different properties, so you can't really expect Bitcoin to replace dollars without a
complete overhaul of the existing financial system. I don't think any state will support this.
Actually, I am not against making it a national currency or even with it but the point is if this is not the goal then what do you mean by Widespread Adoption? Because I don't see a great future with cryptos and fiats going hand in hand.
If you're rooting for a crypto-only financial system, I would assume you have a solution for the dilemma OP described? As for widespread adoption, people can freely use Bitcoin for one purpose, while fiat for another, like what people do now -- is that incompatible with the great future you've envisioned?