Personally I assume they will move on to the GW at some point. It would be unusual to have everything mobilized to do room refurbs and leave a portion of the rooms untouched, IMO. UNLESS the south wing will eventually meet the same fate as the north wing and Disney is content to just let the current room style ride it out until whatever point in time they want to bring the wrecking ball in (IF that were to ever happen).
Other than that, often Disney will let people book first then go adjust later when construction schedules are more certain, so that may be what happens with the GW.
Who knows though!