I don't see he advantage. At our airline the flight crew produce the load sheet on the 25 minute turnaround, implementing this policy will mean longer checkin times and would result in me having to enter up to 180 individual weight figures to produce a load sheet. That is going to be more of a danger than the current system. I think the average weights would prove to be just as accurate, when my family travels I am near to 100 kg, my wife is 52 kg so the average for us is 76kg. So the net effect of all that farting around is that my wife and I pay the same as what we currently do as my ticket is more expensive but hers would be cheaper
You don't see many RPT aircraft falling from the skies due to pax weight inaccuracies, it is not a problem so don't fix it. Also if I am going to pay a premium because of my 1.95m frame then I want a bigger seat and more legroom, surely those short, light people who pay less can make do with a thinner seat and less legroom?