I'm not quite sure I follow

I'm not quite sure I follow what you're trying to do here, but I do have an example of point sprites in the GPUImageCrosshairGenerator, which places crosshairs at locations in an image. Something like that could be replaced with true sprites, and then you could animate them by updating the input positions to a filter like that. The result could be blended into the final image (like I do with the Harris corner detector in the FilterShowcase example).

Interaction with the JavaScript interpreter in WebKit is not something I've done in the past, but I have heard of others doing this. In general, Apple is cool with this kind of interpreted code. They just frown on external means of loading in modules of functionality into applications in ways that work around them getting their cut for the App Store.

Sunset Lake Software - Comments for "A crazy idea?"

I'm not quite sure I follow