Rapids rides typically aren't something that someone is going to buy a ticket explicitly for. Nobody says, "i'm going to IOA for Bluto's" or "i'm going to DAK for Kali" unless they are Annual Passholders. Even still, you'd be hard pressed to ever hear those sentences spoken aloud.
Now it's no secret that water rides are incredibly popular in the Summer at Universal and Disney. However, being that it's a water ride, it's going to need a refurb once a year likely and it won't pull crowds in colder times such as now. It's not that people won't ride this attraction, it's that it's not a ride people will be busting down the gates to get on.
Of course, i'm not sure if SeaWorld is even capable of making a "Gate Buster" attraction with how restricted their budgets are.