I still think there needs to be a maximum weight for total handluggage brought aboard an aircraft.
Essentially, any piece of handluggage has the potential to become a missile during an accident, especially if the overhead lockers either spill out their contents or collapse. Combined with laws of physics, when speed, gravity and weight combine, the consequences can be almost lethal should something as innocent as a 10kg bag fall out onto someone's head, if not a child's!
Furthermore, overhead lockers on all aircraft (that I have worked on at least) have a maximum weight limit for each locker/bin section. What would be the consequences - from an engineering standpoint at least - of these lockers being constantly exposed to excessive weight?
Whilst I'm all for being flexible with hand luggage requirements, etc, I do believe there needs to be some measure of common sense applied.
A carrier I used to work for performed check in for a smaller, pacific airline. One day, a friend of mine was checking in a lady and, as per procedure, asked her to load her trolley bag onto the scales to see if they met requirements.
The bag weighed in at 40kg - and it wasn't big either (looks can be deceiving).
When she opened it, she discovered the lady was carrying several engine components to give to her brother in arrival to fix!
Food for thought!