Personally, I don't think that merging of food mangement etc. would be the thing to do, because I think it is important that each line maintain their distinct personalities.
I have never travelled on RCCL, but what I have been able to gather is that a major problem with them is the inconsistancies between their ships. Some very good, some good, and some bad.
I think this indicates that each ship probably has a different chef overseeing operations leading to these inconsistancies.
Celebrity has one chef, Michael Roux, who is responsible for designing menues, presentations etc., leading to a constant product which most judge as very good. I have sailed on Galaxy, Mercury, and Zenith, and the similarities are very obvious without being boring.
I think what RCCL (and other lines for that matter) might do, is to locate one talented chef and have him/her follow the example of Celebrity with total design responsibilities.
Even "on land" chefs such as Todd English, Wolfgang Puck, Emeril, etc. who are resonsible for numerous restaurants all over the country, are not in attendance at more than one at a time, but their "hand" is basically in every meal.