Diablo 4 has been relatively quiet recently. It's to be expected, in a sense, as fans have a decent picture of what to expect from the game. Right now, Blizzard is probably buckling down and working hard on development. It might still be a long time before the game is out, considering there's no release date attached to it, so patience is required of the fans. However, there's still a particular area that Blizzard has gone many months without filling out: the class roster. Although three classes are public knowledge, there's two more to go.
The longer Blizzard goes without releasing the last two classes, the more speculation abounds. There's a good chance it's still tinkering with a couple new classes for Diablo 4, since every Diablo game to date has featured new classes. However, it's equally plausible that Blizzard is feeling nostalgic and is in the process of reworking old classes for a new game. Not all classes are created equal, though; some of them are much more likely to make a reappearance at launch than others. Here's a quick overview of every class not yet confirmed, and just how likely they are to get an invitation.
Rogue
Diablo 1 had some relatively broad beginnings, with only three classes, all of which were fairly flexible in playstyle rather than locked into particular characteristics. The Rogue was the most flexible of them all, capable of weapon mastery and magic alike, with a particular penchant for ranged weapons. The Rogue might be unlikely just because it's a rather old class that would require a lot of modernizing. On the other hand, Diablo 4 still needs a Dexterity class, and the Rogue might be a fresh and interesting canvas for the developers to work with. Diablo 4 seems like a fairly nostalgic game so far, so the Rogue might have a good chance.
Warrior
Another one of Diablo 1's classes was the Warrior, master of melee weapons but not particularly suited to the use of magic. Anyone looking for a hearty fighter that could additionally sustain himself by repairing equipment would be drawn by the Warrior. Unfortunately, the Warrior doesn't seem likely to return. First, it's a rather generic melee weapon class. Second, it would be hard to make the Warrior stand apart from classes like the Barbarian already confirmed for the game, and third, anyone interested in dominating the battlefield with durability and melee weapons shouldn't hold their breath for a Warrior -- the Barbarian will do.
Monk
Although in recent memory the Monk is probably best known for its appearance at launch in Diablo 3, it first appeared in Diablo: Hellfire, an expansion for the first Diablo game. Monks are melee fighters, but they rely on Dexterity and move through the battlefield with great speed. They're also known for flexibility in playstyle, offering healing and buffs on top of damage. Monks might have a shot at joining Diablo 4, since the game needs a Dexterity user. The problem is that Monks don't offer anything in the way of ranged weaponry, so they might be on hold.
Paladin and Crusader
Diablo 2's Paladin and Diablo 3's Crusader are similar enough that they're worth grouping together. They're both heavily armored melee fighters that supplement their fighting skills with divine might, smiting and impairing enemies. There's definitely a chance for a Paladin or a Crusader in Diablo 4, considering the game doesn't have any holy magic in its roster yet. That would seem essential in a game about warring with demonkind. There's a couple catches, though. Diablo 4 already has a tanky weaponmaster in the Barbarian, and there may be some lore hampering Paladins and Crusaders after Diablo 3. There seems to be a decent chance for one of these classes, but it's hard to say for sure.
Amazon and Demon Hunter
Diablo 2's Amazon and Diablo 3's Demon Hunter might be some of the most likely additions to Diablo 4. Both classes offer weapon-focused and Dexterity-based gameplay, particularly featuring ranged weapons. That's what makes them good candidates. There really isn't anyone that uses bows or crossbows in Diablo 4 yet, which seems like an odd niche to let go unfilled. Odds are good that there'll be room for one of the two in the game. It'll be up to Blizzard to decide whether the Amazon's melee capabilities or the Demon Hunter's dark skills are what Diablo 4 needs.
Assassin
If Blizzard wants to really throw fans for a loop, it could put the Assassin in the game. To date, this class has only appeared in one game as a part of an expansion, and it offers some powerful damage, as well as roguish skills like lockpicking. It could easily become a Dexterity class for Diablo 4. The one hitch might be that the Assassin famously used very specific weapons like claws, rather than more standard weaponry. Diablo classes often have exclusive equipment, but Blizzard might decide the Assassin stands out too much to be in the game at launch.
Necromancer, Witch Doctor, and Wizard
Another pair of classes with a lot of overlap are the Necromancer and the Witch Doctor, as both of them have some mastery over undeath. They're distinguished by the Necromancer's additional mastery over blood and bone, compared to the Witch Doctor's skills with the forces of nature. Since there's already a Druid and a Sorceress, there probably won't be another full spellcaster in the starting list of classes. The Necromancer is slightly more likely than the Witch Doctor, specifically because it doesn't overlap with the Druid in the way that the Witch Doctor does.
Diablo 3's Wizard is also unlikely at launch since there's two casters so far. Like the Witch Doctor, it's also much too similar to another Diablo 4 class: the Sorceress. Blizzard could give the Wizard a second life in a DLC by leaning into its unique aspects, like the Arcane damage type and manipulation of forces like gravity and time. Fans of the Necromancer and the Wizard might have to wait a little while to see them again, but there's still hope to see them again someday.
Potential Surprises
Even though all of these published classes show just how many possibilities there are for the last two classes, all of this could have nothing to do with Diablo 4 in the end. Blizzard could easily surprise players with something that hasn't made it into Diablo games at all before. Blizzard could return to old ideas like the Bard, introducing a nimble dual-wielder that can also use new kinds of magic, or there's also a chance for something totally new like a diabolical Warlock or a new kind of Strength class like a Death Knight. As long as Blizzard keeps quiet about the last two slots, speculation about them will continue to thrive.
Diablo 4 is in development.