UA has had just such a product for many years. It's free for elites and chargeable for everyone else. It has survived several managerial new brooms and has now been copied by AA and DL so I'm guessing the financial numbers work. It was why I chose UA over BA as my preferred carrier for regular TATL trips in the last 10 years. The thought of suffering 31" legroom for 11 hours is horrific.