I believe that Gnome has supported .svg wallpapers for some time. Is there any reason why you're not considering using this? A quick search returned this example. Refresh to see it change, and view the source to see how simple the code is:
Here's an svg wallpaper for KDE which gets closer to what you're looking for:
With an experienced svg artist, it would be rather easy to create a compelling (and dynamic) scene. If Canonical were to provide the layered file of the current wallpaper, perhaps you could set it up as a challenge to attract the attention of some svg experts? I'll even have a go.
Are there any technical issues I haven't considered? Performance? Compatibility? You could of course use a static .jpg as a fallback.
Best,
Joseph