I have to say, I've always loved the idea of a DLR water park, and wondered why it hasn't happened, yet. The region's weather is perfect, the required footprint is relatively small (e.g., part of the existing DTD parking area, for instance), and it would take the pressure off the theme parks in terms of local/AP attendance.
[I hope they do not build a hotel that incorporates the monorail entrance. In fact, I honestly wish the monorail would start functioning as just a roundtrip "ride," without an actual entrance/exit outside of the park (and with outside-world views blocked off by some additional trees and stuff). It's a terrible way for a first-timer to step into Disneyland for the first time. But excuse me, I digress.]