I don’t think the art in itself is great, but because it’s so Anime-like and unique compared to traditional Warcraft art people get too impressed by it. In a typical Anime-like game it would be just another card.
That would be pretty cool. Or even non-legendary minions. Or even Spells or locations or something. Why not? Stormwind was a boss hero in one of the tavern brawls. Just say you have to win 100 matches with that card in your decks and then you unlock it as a hero. Don’t really need emotes.