In thinking about plane loading again, where I suggested they paint the rows in reverse order on the carpet where people line up to board, it occurs to me that in reverse order by row may not be the most efficient boarding order.
When each person gets to their seat, they tend to stop there to put away luggage, blocking other people in their row or further back. If they block the people in their row they make them block the people in the next row and so on, which is not efficient.
The most efficient order might be to do all the windows first (starting with the rear), then the middles and then the aisles. (Modify as appopriate for widebody aircraft.)
This way everybody does the luggage loading in parallel, as nobody is stopping them, then another column moves in. The first-row window passengers might block the last row middles for a short time but it would be minimal.
However...People are notorious in the USA at least for trying to get out of order, even when it slows things down for them and everybody else. They want that overhead space. Normally premium passengers want aisles and this makes them last because it is most efficient.
To do this the row diagram on the floor won't cut it. Everybody needs to be given a big bright card with their number on it, and stand in the square with their number. If people get assigned seats later, give them fractional numbers, I think that can be figured out if the spacing isn't too tight.
The other problem is that of course people seated together are travelling together, though the airline knows that, and the algorithm can be triggered to make things less efficient but more family-friendly.
No doubt some PHD student has already figured out even more optimal orderes for loading.
We do a decently optimal unloading, but not optimal. We'll never get optimal there because everybody has a selfish interest to get off the plane ASAP except those who have checked baggage. This is different from boarding, where everybody's interest is a quick boarding process to shorten the gap from start of boarding to takeoff.
One idea I had to enforce the rules was to set a price, in frequent flyer miles for advance bording. It would really be a penalty but you would call it a fee. If you board ahead of where you should, it deducts 1000 frequent flyer miles from your account. (That's for airlines that scan your boarding pass through a machine as you board.)
This is necessary because gate agents have told me that when they try to turn back people who are boarding ahead of the called section of the plane, they get fistfights sometimes.
Note in response to comment: Southwest does have the best on-time records, in part because they don't assign seats so people naturally get on in a better, though not best order. (The first people on want the front seats.) This is in part what inspired me here, because it seems it shoudl be possible for an assigned seat airline to board as quickly (or quicker) than SWA and still get the benefits of assigned seating. Check the prior article for answers to other questions -- of course people would board with their kids, and pre-boarding is still possible, either overtly or giving the parents a low boarding number. I may be missing something though -- why is it more efficient for those needing extra time to board first? Isn't it more efficient if they board at a time when they would not be blocking anybody?