I always thought that this should be an option on loco's. You could actually choose your seat online (at cost) double for an emergency or bulkhed. Then print it off on line for example a large 12A printed on your confirmation.
Obviously flight number and date of travel match. Passengers in possesion of one of these would be allowed to board first, then the rugby scrum would start. If you turn up late you lose your seat and join the scrum.