I find a frequent contribution to any boarding delay is people stopping to extract reading material or what ever from the single piece of cabin baggage permitted, before putting their bag in the locker. Last Saturday morning for example I watched someone pause in the aisle by my seat and spent the best part of 2 minutes extracting her handbag, magazine and book from her carry on. She seemed completely oblivious that she was holding up everyone behind her. How on earth would any boarding procedure stop that?
(Perhaps if she had been allowed to bring on 2 bags that delay wouldn't have happened
)