Its very clear the OP doesn't understand how programming a map works or designing a video game works at all, if you don't know how th e process functions then how can you say something is possible?... you can't jump off a cliff because where would you go? you can't go for a swim bc
1) waters aren't maped, In real life if you go to California and try to swim 300mi to go somewhere, go ahead you will probably die in the process.

2)water graphics are a whole different graphic ball park. Even droping ps3 support would loose them not just PS3 users, but pc specs would be raised as well. However most people don't want to waist gigs of memory graphics so they can go swim in an ocean, unrealistically, for no reason. If they actually added in invisible walls so that you could swim to places, like midgosmmr, and not go off exploring nothing.

3) 90% of the "sealed off" areas have a quest or npc, or other forms of lore if you read all your quest. The area you talk about is mentioned, also the ruins of beladona, the floating city, and many more. All the new dungeon entrances have been your so called "invisible walls" so logic means that future content will go here.