[dr_win]

IMO, UX is a minor issue. Why would anyone spend hard money before fiat money? (Gresham's law) Also each spending could trigger a separate taxable event (depending on your jurisdiction) and that would be a serious accounting nightmare if done willy-nilly for casual payments.

Bitcoin is a store of value and a payment rail for significant sums. Currently it is not suitable for casual/small retail payments.

In near/mid-term future I expect new banking services to allow people to stay in bitcoin for "savings accounts" and offering traditional fiat credit in "current account" for daily spending (backed by bitcoin in savings account as a collateral). Settlement and transfers between savings and current account to be less frequent and easily trackable for tax purposes. This would allow a person to completely stay out of fiat while still having access to fiat payment infrastructure - this would cost some interest on borrowed fiat which I expect to go pretty low thanks to collateral (bitcoin) liquidity. See companies like BlockFi which are getting close to this model.

[zcopley]

I think Gresham's Law explains it. I could pay a locksmith in bitcoin, but I would rather keep my bitcoin and pay with USD. Bitcoin is harder to get and can be used for purposes that USD cannot (e.g.: donating to financially censored people and organizations).