There are a few obstacles to an Atlantis resort with a water park in Ko 'Olina. While not nearly as good as an Atlantis water park , there is already a water park nearby in Kapolei, plus the newer Wai Kai wave pool in Ewa Beach
There was already a little bit of community opposition to Wai Kai, there would probably be a bit more to yet another water park in West O'ahu, which is the dry side of the island where water usage levels are sometimes a concern.
At any rate, has the new landowner even expressed an interest in building an Atlantis resort with a water park? So far all I've seen is that it was the previous owner's plan.