Sounds like a reasonable approach even if it doesn't happen as quickly as people would like. It's a relief that we (USA) are doing the right thing based on everyone's understanding of the way it worked when they boarded.
But I think there are going to be some changes to how cruise ships are treated going forward. They are not going to be able to skirt US fees, taxes and labor laws and rely on us when they get over their head in the future. I wonder if those poor Caribbean islands will refuse to register ships knowing they would be responsible for dealing with all of the passengers in an emergency... Or if ships would want to be registered somewhere that is incapable of providing support, and if passengers would feel safe boarding anything not under the protection of the USA.