That's where they could use the skybox tech. Show the island in the distance. As for swimming (and later on flying there) they could make it after you go a certain point into the ocean it teleports you far off the coast of the island you were swimming towards. Tho I guess they could change how distance terrain loads and integrate some detailed skyboxes that fade when the terrain itself start loading and just make the distance between zones so huge that you could fly it if you really wanted, but it would be faster by ship.