I would prefer to see a third waterpark first as in summer they are often packed out. Plus it would require much less investment.
What happened to those rumors of smaller niche experiences? Something along the Discovery Cove theme?
Maybe the next park could take on Seaworld?
I think they could solve their busy summer waterpark problems by actually expanding the existing two. I'm sorry, but it's been almost 7 years since Typhoon Lagoon added anything new, and Blizzard Beach has never added one new thing since it's opening back in 1995. Lame. Every other waterpark in the nation has added multiple rides and attractions in that time. For the two busiest in the nation, it only makes sense to add on to them. Being Disney parks, I expect more out of them...especially to help with capacity in some way.
Personally, I would prefer to see an Adventure/unique park concept.