There are many things in the Phase Files ready for a new island. Think, there is still a map icon, models for Isla Mysterious, and a mini-island by the privateer islands that says You can't dock at this island yet. The fog is too thick to see. Don't you think that means there may still be an island on the way? They also recently added the mini-island icons to the map. Thats probably because you'll need to know where they are on the map.