Most of the reports I see on "that other board" are that the Staggered Boarding times are being universally ignored.
Which is something that also is very annoying to me. It means that those people who try to cooperate with the published information are being put at a disadvantage by the pushy ones (like me) who choose to ignore it.
This has gone on for years with the cruise lines publishing material that says boarding begins at 1:00 and then opening the lines at 10:30. It inconveniences those who are not "in the know" and allows people like me to take advantage of knowing it is not true.
Princess is fairly notorious for this sort of misleading publication. Don't EVEN get me started on the lies they tell about St. Petersburg disembarkation.
Saying one thing and then doing another is very bad public relations, IMAO.
How about incentivizing the boarding. Say "Boarding begins at 10:30 AM. A small number of general boarding lines will be in operation, but long wait times may be expected. In order to reduce time spent standing in line, Express Boarding with shortened lines will be available to those who check in on the Staggered Boarding times, and they will receive a special cabin amenities package on boarding at their assigned time."
I think that would work and make everybody -- well, not happy -- but satisfied!