I have been asking everyone and anyone who might have some information. When we were on the Wonder this past November, the CM'S were very tight lipped. My TA has her feelers out, and said she would let me know if she hears anything.
The best information that I have gotten is that it will all depend on the Panama Canal. If the new expansion to the canal is complete the rumor is that the Wonder will be getting the duck tail (they can not add this until the canal expansion is complete because once the tail is on, it will not fit through the canal as it is now ). Once the tail is added, the boat will have the stability to make changes and additions to the pool deck (again just rumors. ..a water splash area, a larger Mickey hand slide, and something similar to the AquaDunk ). If changes are made to the pool deck, there is a chance that changes will be made to the secret deck on deck 7 to make room for the extra water pipes.
Aside from the water play changes, there's also a chance they will be taking one of the staircases in the Atrium out and adding cup holders to the seats in both theaters.
One last thing that was changed on the Magic, but I have not heard anything about on the Wonder is the chandelier in the Atrium. They switched out the one on the Magic, but not sure of the fate of the Wonder's. Personally, I hope they leave it. I am on the side of keeping the classic look.