This is just rumor. But I think you'll see BT as the next slide to be replaced. Also, I read lots of talk about expansion and being land locked. Most people don't realize, the land directly behind the parking lot is all available. Don't be surprised to see some of the parking lot gobbled up by expansion in the future.
I love the dark slide idea, with colored lighting and music/audio inside... But, I'd also love to see a flow rider.... and I'd love to see us triple the length of, and widen the lazy river. BUT, I also know the raintree is in dire need of a rebuild on many of it's play interactions.