It would be insanely epic. Think about it:
Warrior: Samurai, Blademaster, Thunderking, etc.
Hunter: Dark Ranger, Tinker, or Shadowhunter skin, Primalist, and so on
Rogue: Ninja, Saboteur (some sort of tinker spy), etc.
Priest: Cosmic Void skin, or some sort of Scarlet Crusade theme change
Paladin: Firelord or Cosmic Void
Warlock: Necromancer, shadowflame, Red Chaos
Demon hunter: Void, Elune Star skin (Night elf), an’she fire (Blood elf) skin
Monk: Skins based on different celestials, or this black/white old god sludge
Shaman: air bender, voodoo, etc. possible
Mage: time magic (like chromie), mixing fire with frost, and so on.
Druid: more forms, and maybe a turning restoration spells into star priest type spells as balance, and balance spells into some sort of nature theme.