All the resorts have a small outdoor section, even in the Dells, Sandusky, and Niagara, but the main attraction is the indoor park. And there is definitely a role for indoor water parks to fill here in Orlando. It rains nearly every day in summer in the afternoon, sometimes for a while with a nasty storm or two, usually chasing a lot of people out of the water parks a few hours before they close. That's not a concern for an indoor park. The indoor parks are usually open later, as well. The Sandusky Kalahari would be open until 10pm during the summer, and I think GWL was 9 or 10 as well, so people who leave the parks in the evening can still go back to the hotel and enjoy the water park for a few hours. In the summer there are a lot of days where I wouldn't even want to go to a water park with how nasty and hot it is out, but an indoor water park is a nice, consistent temperature every day. Kids want to go back to the hotel for a nap, and you can continue having fun down at the water park. No need to buy a water park and more ticket add on, there's a (really good) water park included in your hotel, where you can come and go to your room as you please, and leaving for a meal isn't as much of a hassle.
There's a lot of upside to the indoor model, and I think guests will pick up on that quickly. Just wish GWL sold day passes.