Restaurants are a little different than cruiseships. The smoker only has to go an hour or two without a cigarette and can even run outside for a smoke if they feel the need. Quite a bit different than being trapped on a non-smoking ship for 24 hours a day.
No doubt, smoking is becoming less popular and someday there will not even be a need to have this discussion because there won't be enough smokers left. However, until the day comes when banning smoking becomes more profitable for the cruiselines than allowing it, I doubt we will see any major changes. And I don't think that day is going to come anytime real soon.
So far, all the ships I have been on (mostly Princess with a few Carnival and Celebrity) have had pretty liberal smoking rules with smoking allowed in all cabins, on one side of outdoor decks, and in designated areas (which seemed to be plentiful) of most bars and lounges. I don't see this changing anytime soon. The cruiselines have too much to lose and nothing to gain. I thank the Carnival Paradise has already proven that.