In Brazil, with a huge informal economy, you can now find all sorts of small street vendors with a card reader. Also the government has successfully rolled out Pix less than 2yrs ago, with now 50% of the population as registered users. Pix is the smartphone payment protocol which has basically nuked cash transactions countrywide, or at least where mobile networks work.
So, at least in Brazil, card readers are already on the way out for informal workers, and even some SMBs, and Pix with its QR codes and phone numbers are in.
This process has started in Puerto Rico, too. People still mostly use cash, but almost every vendor these days has ATH-Movil, a phone-based payment system through your bank.
So, at least in Brazil, card readers are already on the way out for informal workers, and even some SMBs, and Pix with its QR codes and phone numbers are in.