I doubt it, but they could get more popular. You can do a decent Caribbean cruise in 7 days, while other than an Alaska cruise, the others are longer and more costly, therefore the main reasons why Caribbean cruises will always remain popular for the average working people, with or without family/kids.
I find it difficult to get enough vacation days all together to do a longer cruise, may-be someday when I'm not working full time or better yet retired.