I found writing something like this to be one of the natural steps in a pure javascript client. People can do a lot more than they realize with javascript. On my website, http://www.classbug.com , the fade effects, the transition effects, and the disclosure button rotations are all done with an animating value from 0 to 1 (though not using KochiKit.Animator).
That's only the beginning though. Dynamic tree views, color selectors, etc.. You should build a framework of components to insert into your web application.