but a regular Bitcoin payment doesn't seem viable. Ignoring the issue of high fees, the confirmation time seems to be the problem. With average block creation times of around 10 minutes, it can take up to 20 minutes or so for a transaction to get into a block, and that is providing that it gets into the next creation, and it isn't an orphan. That seems far too long if you are waiting in a payment queue.
It is true that regular Bitcoin payment method does not look viable for the quick services. If we put LN out of question (seems fair enough as it is still in testing phase) then subscription can be viable method for these kind of services. (where user prepaid for 30 coffee).
But real challenge is not how to pay the coffee but what you are paying for coffee. I do not think as a coffee lover you will like the idea of daily calculating the price of your coffee in bitcoin vs fixed price in fiat. Bitcoin need to be mass adopted to solve the price fluctuation problem where worth of bitcoin is not pegged with any fiat currency and we can independently purchase articles on fixed price of bitcoin.
Without any LN or a system that can scale current system TPS and confirmation time, buying a coffee is feasible but not convenient.