The automated attack setup I'm envisioning is something like: 18 year old buys a cheapo laptop + phone and connects the two over ADB or some purpose built automation app (think appium). 18 year old puts the phone on a tripod pointed at the laptop screen. 14 year olds at school pay $10 a year for use of the service and install a browser extension that forwards the QR codes from whichever service they wanna use to the 18 year old's computer. Changing every couple of seconds is not an issue here, they all live in the same city and have <10ms ping.

The only high friction part of this is that someone needs to write the software for it, but that doesn't seem like all that difficult of a project and open source solutions are likely to appear within weeks of social media requiring it. If there really is no information shared with the other party beyond "yup, user is over the age of maturity" you could even run this as a free public TOR service without fear of ever getting caught.