I don't think it would work. Unlike WoW, FFXIV has a singular linear main story. That requires those old areas to be there.

While they could, theoretically, update the old maps to allow flying, they aren't going to mess with their linear story by throwing another cataclysm at the ARR zones and replacing them the same way Cataclysm did to WoW. WoW's story isn't nearly so rigidly structured so they could more easily do it than FFXIV could.