for the business owner, including the tax problem, you could maybe have a aintermediary, who pays the part of restaurants bills, equivalent of income that has come threw lightning. And find a way to agree on that legally. Then you have easy enough way for a business to withstand weird payment - adoption. You then have to figure a way to be a sustainable intermediary, who pays someone's bill for being a QR code on tables in the restaurant.
Which is what a company Qerko does:
Haven't tried it, but I use the service often with fiat and it's awesome. And they say they are testing it, so you need to activate the feature. Which is worthless for UX, but still. Don't know the legal perspective.