The problem with boarding planes is that people completely ignore when they're supposed to board and immediately line up as soon as boarding starts.
I fly all the time and as soon as boarding starts for the last N rows more than half of the passengers line up, in a completely random fashion. It's as if people are unnerved by waiting while other people are boarding, even though everyone has a specific seat.
People would have to be trained into some form of orderly boarding before improving on the theory has a hope of helping.
Luckily, people are easily trained by enforcing the rules. If airlines actually enforced zone rules, people would learn that it's easier to obey them than to chance the hangup they would cause by a failed attempt to cheat them.
I don't think the average person flies frequently enough to really get a feel for the rules. They hear "my flight is boarding" and feel like the flight will leave without them if they don't hang around the gate. Even I get a little worried when I arrive after boarding has begun (and I fly at least once a month).
The demographic that flies frequently enough to learn the rules probably already has elite status, and gets to board first anyway.
(I imagine there is a small number of people that fly frequently, know they need to beat the rush to get their carry-on stowed, but for some reason don't have elite status. Maybe enforcing the rules would train these people -- but there's really no incentive for them to not break the rules, so they will probably try anyway.)
I fly all the time and as soon as boarding starts for the last N rows more than half of the passengers line up, in a completely random fashion. It's as if people are unnerved by waiting while other people are boarding, even though everyone has a specific seat.
People would have to be trained into some form of orderly boarding before improving on the theory has a hope of helping.