I guess we could do that although I'm not sure who would reasonably venture out that far to train fishing. Even in f2p one must bypass the Musa point fishing spot and risk a tidbit of damage from monsters in the volcano before getting to that burnt island
It's a f2p training spot; specifically the moss giants and lesser demons; and it's an island in the middle of the ocean, so adding a fishing spot would fit thematically and help f2p players out with food as traveling to the area is a pain.