Yet another reason why they really ought to just weigh passengers + baggage … and charge them accordingly. But you can’t do that because fat-shaming.
If they would implement this system, the result would probably be that light people pay the same as now and heavy people have to pay extra.
I would really like to see airlines having a scale at their ticketing counter and telling people they are so fat they have to pay more. I would definitely ask for hazard pay if I was a ticketing agent.