As cute as anthropomorphic ears would be, no. It makes no sense in-universe or out. In-universe, they're useless. They wouldn't be able to be worn under the helmet, they wouldn't make sense being worn over a helmet. And while you could put them ON the helm, what's the point of that? Ears like that raise the profile of the helmet. And anyway, what manufacturer would make a helm like that? For what reason? We're fighting a war. While WE care about looks, our Guardian probably wouldn't. Out-of-universe, it still makes no sense. Why spend the time on them? What does it add to the game? What kind of audience would show interest in these? Furries and those interested in cute things? Well, sure, but where does the audience that likes Destiny and the audience that likes cat ears intersect? Is it worth the investment to make them? TL;DR: No.