For WYSIWYG images and animation, perhaps Blender http://www.blender.org/ offers some kind of export format that a JS library could use? Perhaps export COLLADA (open standard 2D and 3D graphics and animation file format) to be consumed by something like http://threejs.org/ ?
The advanatage of using something like Blender is that it can export to a wide range of file formats and so if your target platform changes, you don't have to start from scratch (again). Whatever platform you're targeting, be it in Flash, Java, HTML5 + JS, rendered video, etc., the same source files will give you the appropriate output format.
Again, doing it this way and exporting to HTML5 + JS will more than likely crash even the newer, more powerful mobile devices (phones and tablets). Since Windows desktop, Apple OS X, and almost all Flavours of Linux already support Flash and Java, which manage multithreading (concurreny) and memory, which are absolutely necessary for high quality graphics and animation, it seems a bit redundant to go down this route.