that is going to be interesting.
i am working at the gate for BA and even if we really try hard to avoid big bags to go into the cabin, it is a total mess when flights are fully booked. most passengers have bags that are the right size (we have those things where they have to put them in to check the size), but if every passenger has one of those there is not enough space in the cabin.
we have the advise that luggage over a certain weight is not allowed due to savety. so even if business pax are allowed to have 18kg in total (handluggage) it has to be split into 2 bags of 9kg. so why is it suddenly ok to have heavier bags in the overhead lockers?