i agree with you and only want to add another idea: Diving
An underwaterworld with riffs, turtels, new fish, shellfish and treasures would make this game more diversified and amazing
Now this is AS ambitious as the "Islands" idea. I am not saying it's bad, but how would we get past the Shark menacing us? I would say the idea has many parts that must be worked out, but lets say there is an underwater world. Perhaps we can use underwater riffs to generate electricity.
How you can make electricity with riffs , seems not realistic. To your first part i wanna say that i know my is idea ambitious and its just an idea but i think its important for developers to know aproximately what should coming out at the end of developing