Disclaimer: we're merely coming up with ideas for a 4th spec for each class, does not mean there will be
Warrior:Berserker; damage spec revolves around throwing your weapons/ shield at enemies, will have a passive that has you character throw weapons when target is out of range, will be able to duel wield 2 handed weapons, suggested weapons: spears, 2-handed axes
Warlock: Corruption; tank spec, playstyle turns the player into a mini raid boss, with AoE drains, fel lightning, will have shapeshift that allows player to turn into a demon(a lore reason behind this could be that the warlock absorbed some of sargeras' corruption) male form would have a beast-like Sha kind of look, while female form would resemble a sha covered elf or human, each with differences and armor resembling race of warlock, corrupted breath/beam(channeled), and Devil's Mark(DoT effect curse) suggested weapons: fist weapon/swords/staves
Paladin: Knight; mobile tanking spec, would focus on sweeping, and charging strikes, from atop your class mount, would have a passive similar to a baby Titan
s grip, would allow you to wield a 2 hander in one hand, and a 1handed or shield in the other, but not duel 2handers(thought this would fit the paladin better than the Warrior)
Shaman: Earth warden; tank spec, would focus on AoE tremors and knockbacks, duel wielding spec
Rogue: Strategist/Gambler; damage spec, focused around tactical strikes , and taking strategic risks, would focus evenly on ranged and melee combat
Monk: Hopebringer; ranged damage casting spec centered around survival
Druid: already have one
Demon Hunter: I have no idea
Mage: Conjuring; damage spec, focused on summoning arcane constructs from atop a mount(to fill the mounted wizard niche)
Death Knight; Flame; melee damage spec, focused around DoT effects(some of the older scourge were associated with fire), would duel wield
Hunter: Pursuit; damage spec, focuses on pursuing prey from atop a mount, would focus on ranged abilities, and preventing prey from escaping
Priest: Inquisitor; damage spec, focuses on DoT spells and healing