Raising the seabed is a very, very cool idea. Partly made popular by GoldenYak, I think?
But I think it'd get old fairly quickly. Exploring these coral reefs and sunken chasms will only feel dangerous, bizarre, and immersive if they are in fact submerged deep below water. Otherwise you won't feel isolated, as if being a thousand miles from safety. That "plunge" into the unknown is precisely what made Vashj'ir such an amazing experience for me. That said, I get that underwater content isn't for everybody, and raising the seabed would create a cool middle ground. Something we haven't seen in the past.
Had I the choice, I would raise one of the underwater zones to the surface, perhaps at max level once the questing is done. For instance, we could explore Queen Azshara's city of Nazjatar while questing. Then, at some point, she raises the city to the surface in order to launch the full might of her invasion, and it becomes a daily quest zone for us.