the best use case in the united states is as an alternative to gold, as in store of value. that is crypto's killer app. the payment system cannot compete with centralized ones, unless you're looking to buy black market goods.

financial products like ATM's, credit cards were very slow to achieve widespread adoption. like a decade each.

its possible consumers will start buying a bit of crypto instead of lottery tickets. thats the only way i see half the population using bitcoin/ether/etc.