(Suggestion) Fang should really just be able to turn super.
To my understanding, what's holding Tails and Amy back from gaining super forms is the fact that there's currently nothing they benefit from having them, aside from invincibility & faster speeds. However, due to the way that fang's bounce is programmed, he already gets a major boost to it while super, and IMO, said boost is more then enough to warrant him gaining the ability to access super forms.