If existing PoS / payment terminals added btc option and merchant got paid in bitcoin, I think many would accept. Potential new customers and lower fees than credit cards, not much downside. Currently some merchants use e.g.

🇨🇭 Swiss Bitcoin Pay

Accept Bitcoin in your Business. The simple way. Worldwide. Free to start. No hardware. Non-custodial.

and get paid in fiat but it requires a separate payment terminal and is always a bit of hassle, not great for supermarkets.