It doesn't need to be animated, really. It rotates the picture every shot anyway, which is good enough to make it look animated.
EDIT: Btw, the reason AC doesn't support GIFs is probably because GIF is a proprietary format, and it's also amazingly crap quality. If AC was going to support an animated image format, then they'd probably be best going for animated PNG (http://animatedpng.com/), which is opensource (I think). They could also just go for an opensource video format, instead of an animated image format, but I don't know any of those off the top of my head.
EDIT: Btw, the reason AC doesn't support GIFs is probably because GIF is a proprietary format, and it's also amazingly crap quality. If AC was going to support an animated image format, then they'd probably be best going for animated PNG (http://animatedpng.com/), which is opensource (I think). They could also just go for an opensource video format, instead of an animated image format, but I don't know any of those off the top of my head.