Most of the examples of Lightning that I've seen involve frequent transactions between small numbers of parties. How would this work in a retail transaction? For example, if I want to buy a cup of coffee from a shop that I visit infrequently?
But as you said, coffee shop needs some path to you to make that feasible. So then you get BTCVisa (c) or whatever, which is a channel provider that has built a network of channels open with lots of vendors. If you open a channel with them then you get to benefit from getting to use the wallet you already have. There is cross-channel routing of course so maybe that doesn't happen but it seems like a natural result.
LN is neat in concept, but I'm not sure I really see the point compared to Bitcoin cash or the like that just say scale on chain. I guess we'll see.
So, most likely the coffee shop has just one or a few channels open to popular exchanges or dedicated LN services. You open a channel either directly or indirectly to the same exchange / service.