Not all that area is expansion, some is for park support and such.
I think Universal is waiting for guest feedback and wait times on attractions before making a choice. Even if they decided in late 2017 ProSlide might not be able to deliver till 2019.
What I think the expansion could be:
- Larger raft water coaster, similar to Mamoth at Holiday World
- Raft racing slides
- Family body slides
- Additional kids water playgroud
- And/or additional food, drink, restrooms, beach area with chairs, and cabanas