Zooplantman beat me to it! Not crazy about everything I see, and was frankly hoping for more, but it is at least movement in the direction of new development. Also as a 20 year master plan I assume it will be subject to refinement and change as public reaction is received, and when actual construction plans have to be drawn. Very glad to read on the zoo's site that the first project will be a new Tiger habitat as part of the Asian "Lost Kingdoms" section. If it looks anything like the rendering, it should be great. The rendering kind of reminded me of the Jaguar exhibit at the Woodland Park Zoo in Seattle.
I'm guessing they picked "Sheepy Hollow" as a cute little nod to American writer Washington Irving. He actually has a tie to the Tulsa area. He was part of an expedition in the Indian Territory in the early 19th Century. They camped along the Arkansas River in what is now Tulsa County and the group collected wild honey there. That event and the entire journey are chronicled in his book "A Tour of the Prairie." There is now a public park named for him near the campsite, complete with a statue of him, in the Tulsa suburb of Bixby.