Here's my prediction:
Magic: Stays in the Bahamas/Caribbean, with an occasional trip to Bermuda. She will move around a lot with some combo of Fort Lauderdale, New Orleans, Galveston, and San Juan. Perhaps Port Canaveral. I think Disney wants her to stay closer to home.
Wonder: Remains the West Coast ship. No real changes. Mexico, Alaska, Hawaii, Australia from various ports. I will be surprised if she ever sails in the Atlantic Ocean again. She is fitted for the Alaska sailings and has been very popular over there.
Dream: Remains the same, which is what the Magic did for a long time. Bahamas/Caribbean from Fort Lauderdale, Europe from various ports, and a fall season of Canada and Bermuda from NYC.
Fantasy: Splits time between Mexico and Bahamas/Caribbean. She is moved to Fort Lauderdale to do a mix of itineraries while the Wonder does the Mexico trips. Then when the Wonder moves to Alaska/Hawaii/Australia, she takes over in San Diego until the Wonder comes back.