I know a guy who sideloaded BTCpayServer onto a Toast POS terminal st a couple fast food restaurants, but it's just a website. A $60 tablet or old smart phone would work.
I have Zeus on android that is linked to Square. I am talking mass appeal. National marketing.
Jack Mallers tried that, but suits are a tough nut to crack. Small businesses will also be hard, but I'm optimistic. We need better marketing and a bitcoin geek squad willing to help set up infrastructure.