Re grandfathering - I haven't dug into it to look (and seek confirmation), but I was told a while back that if the 737 ng had modern door sizes (eg A320), then there would be one or two rows fewer in the cabin. That's 6-12 pax every sector for the life of the aircraft. That's a (theoretical) lot of $$$.
Last edited by compressor stall; 23rd Dec 2019 at 10:32.