Looking at the "Updated Subclass" UA with Warcraft Context

 In October of last year, we got an Unearthed Arcana that had a notably bland title: "Updated Subclasses." Nothing thematic tying them together.

These were all riffs on subclasses that had already appeared in 5E. The Spiritual Guardian, Warrior of Intoxication, and Storm Herald had all appeared (maybe with slightly different names) in Xanathar's Guide to Everything, and the Oathbreaker had been a subclass in the 2014 DMG meant for villainous NPCs (though I strongly advise DMs to use normal stat blocks rather than full character builds for NPCs.)

I had thought at the time that this was likely to presage an upcoming "of Everything"-style book that would just give us a bunch of new subclasses for 5.5. However, now that we know about D&D's crossover book with World of Warcraft, it's all coming into focus.

One of the really interesting things that seems implied by the subclasses being presented is that D&D will interpret WoW's Shaman class as Barbarians. Now, the Shaman in WoW is primarily a spellcaster, tied to primordial elements and the spirit world. In a lot of ways, they're similar to Druids as a "nature"-based class, but while Druids are focused more on living things (though also a bit of a celestial sun-and-moon-and-stars theme) Shamans are focused on the raw elements, throwing lava and lightning around.

Of the three "specs" for Shamans, two stand at range, casting spells. Elemental Shamans send out bolts of lightning and hurl lava, while Restoration Shamans use the power of water primarily to send waves of healing energy. (In WoW, healing works very differently - if you're the healer, you're probably spending most of your time casting healing spells, and only if your party is in great shape do you every turn your attention to damaging enemies - though some healing specs will incorporate damaging enemies as part of their healing strategy.) The third spec, Enhancement, is the one where you get into melee, dual-wielding and charging (or enhancing) your weapons with elemental power and also casting spells in melee.

I think that both the Spiritual Guardian and Storm Herald subclasses are thematically tied to the Shaman as a class, but it's interesting because a class that in WoW is very much focused on casting spells is, in D&D, going to be the class that truly can't (with the exception of Spiritual Guardian's outside-of-combat ritual spells).

At Gamecon, I believe they announced that the Storm Herald was getting a top-to-bottom redesign, which is probably for the best as the old subclass and its UA version were both cool conceptually but mechanically kind of sucked. 

The Warrior of Intoxication is clearly tied to WoW's Brewmaster Monk. In WoW, this is the tanking spec for Monks, thematically using Drunken Boxing techniques to stagger the damage they take, and then cleanse that "staggered" damage with purifying brews (essentially, the way it works is that you only take part of the damage of each hit you land, while the rest is spread out over time. On its own this makes you easier to heal, but you can also effectively get your "damage debt" forgiven by using a particular ability). It's not pure martial arts, though: Brewmaster Monks toss barrels of brew around, splashing enemies and then using Breath of Fire to ignite the alcohol and do damage over time against them.

Now, in this context, the Oathbreaker Paladin is surely what they were using to secretly test out the Oath of the Ebon Blade, which is how the book will represent Death Knights. In WoW, Death Knights are a full class with three different specs (the lore behind them is that your character was a hero of Azeroth who was then slain by the Scourge and selected to be raised as a Death Knight. However, while you fight for the Scourge in the starting experience, an attack on Light's Hope Chapel, a bastion of the heroic Argent Dawn faction, makes you realize that A: you were set up by the Lich King as fodder to draw out the Paladin Tirion Fordring, and B: that you have regained your free will and are not bound to serve the Scourge, allowing you to reform and become a heroic adventurer. (Note that if you place a race that was added post-Cataclysm, you don't get such a dramatic introduction and are just a heroic Death Knight from the start, serving the far more benevolent Lich King, Bolvar Fordragon).

Anyway, what is likely the playtest for the Oath of the Ebon Blade allows you to summon undead minions (likely 1 initially, and then 2 if you can get your Charisma modifier up to +4 or 5). This, I think, is meant to give you something equivalent to the WoW Death Knight's Raise Dead. For two of its specs, the tank-focused Blood spec and damage-focused Frost, the ghoul you raise with this spell acts as a temporary pet. For Unholy, the other damage spec, this is a permanent pet that fights alongside you, and some of your abilities can enhance its attacks.

I will say that I don't know how relevant this will be at higher levels given that the stat blocks don't scale.

It's interesting here that this UA actually included the Cavalier as well. I don't think the Cavalier was ever a terribly popular subclass, and it's not super obvious what it would be equivalent to for WoW. Possibly the Protection Warrior, which is the tank spec for Warriors (basically the WoW version of the Fighter, though I'd argue the flavor of the Fury Warrior is more like a Barbarian). Perhaps this subclass didn't score well enough to make it into the book.

Now, I will say that they only described the Spiritual Guardian, Swashbuckler, and Mystic Brews subclasses as updates to existing subclasses (Mystic Brews being the clearly better name for the Intoxication Monk). While the Path of the Elements is likely to have some similar flavor to the Storm Herald, as mentioned above, it's expected to be a total mechanical overhaul. But they also don't describe the Oath of the Ebon Blade as being an update, so perhaps it's less similar to this Oathbreaker than I thought.