I can do that with my 200-500 now. Of course, I consider even MY 200-500 lens to be too big to lug around Disney World - I couldn't imagine this behemoth! You'd need a motorized cart just for the lens. Then again, for the price it should COME with its own motorized cart.
While I'll admit to being a bit jealous about having F2.8 at 500mm (versus my current lens' maximum of F6.3), for a price under $1,000 and a hand-holdable weight, I'll stick with my current one. And 1,000mm at F5.6, not to mention the crop factor from my APSC sensor which would push to 1500mm optically...well that's just crazy nuts! You could not only shoot the carousel from the train station, but you could focus on the gold tooth in the smile of a person riding it!