I think the airlines will be highly interested in your idea! Because...
Maybe they can now put 7 seats on a single aisle plane, or 10 across in 777, 12 across in a 747. More revenue! The seats can now be even narrower because your arm has somewhere to go now!!!
How about give everybody a mattress instead? People will be happy with beds, and they can load people into drawers like some Tokyo hotels. Maybe a A380 can hold over 1,000 people that way with people stacked 3-4 high in the cabin.
