I think swimming is an appropriate thing to add to this MMO. In fact, all MMO's should have it, and yet I can't think of any mainstream ones that don't sides FFXI.

Yes, player's should be able to swim, down below and over and above. The problem is, SE didn't make the ocean big enough to swim from one island to another. It's all controlled by a fixed camera angle that moves the boat from one area to another. That's why there are loading screens when docking.

I think that if the player were to swim, it would add a third dimension to player involvement in the world of Eorzea, something I think this world is currently lacking.

Let's not forget that the ocean might actually be more vibrant than looking at the same tree over and over and over.....