Story mode just doesn't seem right for this type of game. Regarding multiplayer, the dev has said that the studio is currently small thus they can't do multiplayer so currently, it is not a planned feature and I don't think will be implemented for a long time. Concerning sized islands to go to, that would ruin the very thing that made this game unique. Many games already do this thus if this game did it, it would not be as unique. Finally, diving in the ocean, many games already do this (Subnautica being a popular one).