As it stands, every tier of resources has its own island(s) except Tier IV:
Tier I: Lesser Aradoth; Genevia
Tier II: Abandoned Isle; Scorpion Island
Tier III: Trandalar
Tier V: Saritova
Please allow me to petition strongly for the addition of a Tier IV island. Presently, there is only ONE place in all of Istaria to gather either Maple or Bright Essence--Feladan. So if there is only meager competition for the trees or wisps there, you have to just find something else to work on. Indeed, I can think of no other resources of any tier which only have one spawning area.
So please, could you put a Tier IV island with all Tier IV resources somewhere on your planning radar?