I honestly think we should have animated avatars. But they introduce some accessibility problems that can't be controlled by the forum, one of them being potentially excessive motion and users who have problems with it. Also, flashing high contrast colours. You get the jist. These would have to be moderated a posteriori and could at that point have done damage to other users. Since they are external assets, i don't think there is any easy way to validate whether each individual file would be problematic before they're set as active.