If Disney is homeporting in Galveston, it certainly is not going to be one of the two newbuilds. The itineraries on the Dream and Fantasy (as shown on their website) are the following:
Dream - 3, 4, and 5 day Bahamas
Fantasy - 7 day Eastern/Western Caribbean
It also appears the Magic and Wonder are pretty set on scheduling too:
Magic - Mediterranean, Bahamas, Transatlantic Crossings, still Canaveral Based
Wonder - Mexican Riviera/Alaska
Of course itineraries are subject to change, so I'm curious to see if they [Disney] actually do make a move to Galveston.