Sort of like the shield and other systems put in place to prevent you from seeing certain avatars you don't want to see, but flipped around. You could, for example, make it so that only friends will see your avatar and anyone else will see your fallback/impostor.
I see this having two benefits:
  1. Provide a layer of protection from rippers.
  2. Allow you to use more low performance avatars in public worlds without being a burden to other random players in the same world.