Certainly an interesting story, and good work from the guy for the work he's put into researching this - clearly for information purposes and not for gross gain.
At the end of the day if people do this they are fraudulently gaining access to something they shouldn't. In the grand scheme of things it may not seem like anyone loses, but if every economy customer did this then there would be chaos, and someone needs to pay for all of those buffets and drinks!
The easiest and cheapest of resolutions is for the staff to properly check eligibility, by insisting to see your boarding pass, whether it is paper or an app, and not just allowing a full screen photo of a QR code which could have come from anywhere. Correct me if I'm wrong, the QR code is only valid if it is shown within the airline's app, full digital boarding pass (e.g. Passport on iOS) or if the person can reasonably explain that it is genuine.
The long term solution I guess is for those airlines that have more generalised checking of boarding cards, is to update the reading technology and software they use to drill down and only validate genuine flight tickets for +/− 24 hours the time of attempted entry. I however no nothing about what process they use for validation, I am a tech geek but in a different field!