Also, "hundreds of kilograms" is not a lot if you consider how much the rest of the plane weighs --- a 737 MAX is ~100k lbs empty, so this is less than 1% of its empty weight, and a 747 is between 300-500k lbs empty.
Then again, given how airlines would cram in even 1 more passenger if they could, and the absolute minimum robustness of other mechanisms on a plane as a result of weight-saving, I think they will still chase after <1% gains.
Then again, given how airlines would cram in even 1 more passenger if they could, and the absolute minimum robustness of other mechanisms on a plane as a result of weight-saving, I think they will still chase after <1% gains.