The major changes that affect the ship's shape won't happen until Disney is sure the Panama Canal locks are finished and running. That would be, most likely, the AquaDunk and other water features.
They have been doing some minor "re imagining" already - new beds, and changes in the rooms. The next dry dock is scheduled for fall 2016, there's some speculation that they could do some of the interior changes at that time (Carioca's; kid's clubs; D Lounge and the like). Don't know for sure whether they will or not.
retro fitting the interior rooms with Magic Portholes involves a ton of wiring: Power and video/network cable at a minimum. Not counting the servers and video cameras to run the system.
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