I have a question too. Since opening the payment channel requires an on chain transaction does that incur its own set of fees? If I walk into a coffee shop and want to buy a coffee but don't have a payment channel open yet doesn't that mean I could have to wait minutes/hours before the payment channel is ready?
The on-chain transaction to open a payment channel is treated like any other Bitcoin transaction, so the fees are pretty much the same -- except that it can get used for multiple transactions instead of just a single one. So yes, it would probably make sense to have a payment channel ready before entering the coffee shop.
Taking transactions off-chain is likely to free up blockspace however, so 0-conf transactions may become viable again. However I'm not sure what possible attack vectors would come with accepting 0-conf transactions for opening a payment channel.