Every plane I've been on in the last decade already sorts people by "boarding groups" which are relatively fine-grained. They won't let you onto the boarding ra

Every plane I've been on in the last decade already sorts people by "boarding groups" which are relatively fine-grained. They won't let you onto the boarding ramp unless you're in the correct group, which they check by scanning your boarding pass. All they would have to do is make those boarding groups be based on your seating position instead of how much extra money you paid.