In the BeOS days there was an app (sorry, forgotten the name) that displayed an animation as a kind of layer between the desktop and the applications. Personally, I found it incredibly annoying.
We know from a recent thread that MediaPlayer can play animated Gifs with a little cheating on the MIME types. So all you really need to ask for is to make MediaPlayer able to spawn desktop replicants. I have no idea how hard that would actually be.