I'm not sure about slide concepts, I think the park would need to take a serious look at what Aquatica has done. They really took waterparks to a whole new level.
The lazy rivers are an experience in themselves, along with the slides!http://www.aquaticabyseaworld.com/RideList.aspx
Omaka Rocka, Tassie's Twisters and Walhalla Wave stood out as my favorites.
A multi person ride would be great for familys. Think Teamboat Springs at Blizzard Beach (on a much smaller scale!!)