I just think this will take all aspects of the game into a new stage. It will define the game world, such as islands inhabited by say Odditown (Hogwarts island) or Dis and key land areas which will be fought over because they are closer to the mountain for example. areas which will become war zones and areas for hermits which will be deemed safer as you do not have raiding factions in the areas.
It will force allied factions to congregate into similar areas and will pave a way perfectly for kingdom implementation, although I don't know how I feel kingdoms personally...
Not to mention port trading possibilities, this is where knarrs will really become useful and raids of those ports also by Knarrs.
I have attached some rather random island maps I have seen.
This one is larger, please zoom out to see whole map.