I am not aware of anyone working on this.
There is no plan to add animated GIF support in Flarum core since our image resizing library doesn't support resizing animated GIFs. If an alternate library exists, a proposal to switch it is welcome, but this would probably have to wait for Flarum 2.x unless its API is fully compatible with Intervention, the current image library.
You can still manually put a GIF in the
avatars folder and manually update the user avatar path (can also be set to an external, fully qualified URL), but you have to take care of verifying the image size is not too large for performance and does not contain malicious code the webserver might execute.