Based on what we've seen so far with splatbooks (the Elemental Evil Adventurer's Handbook) I imagine we're going to see more accessories based around themes and adventures rather than classes. Which will make it much, much harder to find a place for some of the more generic subclasses. Elemental Evil will be a great place for an elemental druid or Primordial pact warlock, but it should NOT be the place for something like an enchanter bard.
Having to hunt for content that is not in an obvious location is awkward and should be avoided. That's half of rules bloat.
Barbarian
Path of Twin Fury. Two weapons. This needs to be a thing, because it currently doesn't mesh well with the critical buffing feature and barbarians lack the weapon focus of other martial classes while also being feat starved.
Path of the Fetish. Drawing strength from fallen foes. These might be trophies or the consumption of enemy's hearts.
Path of the Blood Mage. The equivalent of the arcane trickster or eldritch knight, adding some sorcerer to the barbarian.
Bard
College of Manipulator. The bard that fascinates and charms opponents. The enchanter build.
College of Trickery. The illusionist/summoner build, possibly working with shadowstuff to conjure creatures or generate phantasms.
College of Respite. The buffing bard, who makes everyone better, and has spells focused around aiding the party.
Cleric
I don't see the need for many new cleric builds. Most gods seem to be covered, and adding new subclasses/domains just means having to retcon the list of gods in the PHB, which should be avoided.
That said, there are a few small gaps in god
portfolios. I think elements might be handy: Fire Domain, Water Domain (with cold), and Earth Domain, since we already have Tempest covered. There's a lot of historical deities tied to the elements, so this makes sense; not all fire gods work as sun/light gods. For example, the lack of a domain appropriate to smiths means Moradin and Reorx are gods of knowledge, which is weird.
Druid
Circle of the Beast. This is pretty obvious and a glaring omission, especially as all the druid art includes an animal companion. Give them an animal companion, the ability to talk to animals, and summon minor animals (even if non-combatants).
Circle of the Elements. Almost as obvious. A druid tied to the four elements. An Avatar if you will.
Circle of the Spirit. The shaman type character that deals with the spirit world, fey, and the like. They might be able to talk to spirits, summon spirits, interact with other planes, etc.
Fighter
Battlemind. When we get psionics, the psion equivalent of the eldritch knight would be cool. And the name works better than "psychic warrior".
I don't think we need many new subclasses at the moment since the fighter is defined by its mechanics: simple or complex. More maneuvers are all that are needed, but finding a place for those would be cool.
It'd be neat to have some more tanking, some mounted combat, and the like.
Monk
Way of the Drunken Boxer. Lots of bobbing and weaving, erratic movement, with tricks like breathing fire or resisting damage. Because it's fun.
Way of the Raised Staff. The monk that relies on monastic weaponry, especially two-handed ones like the quarterstaff, spear, monk's spade, etc. Maybe throw in some improvised weapon bonuses as well, for the Jackie Chan type character that fights with whatever's handy.
Paladin
I don't see the need for many other oaths. We're pretty well covered with paladin archetypes at the moment. Except possibly an "oathbreaker" subclass for paladins that stray but don't go full antipaladin.
Ranger
Trapper. The ranger that is good at making tracks, ambushes, hiding, and the like. Possibly with some skill use, dipping into bard/rogue territory.
Delver. Instead of focusing on the aboveground, this ranger is all about the Underdark and dungeons.
To expand the ranger I'd really like to see more spells that are not spells. Spells they can take that can be flavoured as mundane abilities. Or a subclass ability that lets them burn a spell to recharge an ability, like the paladin's smite.
Rogue
Conman. The Charisma-based rogue that is less about robbery or murder and more about social skills such as deception, trickery, and bluff. They might be able to hand off their sneak attack to an ally and otherwise buff the party without directly making with the stabbity stabbity.
Investigator. Like the above, the subclass that is about assisting and less about the old ultraviolence.
Sorcerer
Fey Bloodline. If any ancestry would convey innate magical powers, it would be faeries
Primal Sorcery. Lots of elemental effects and powers. Works nicely for Dragonlance as well.
Warlock
Draconic Pact. Strike a deal with a dragon and become infused with its essence.
Primordial Pact. Making a deal with the anti-gods. Another dash of elements.
Wizard
We don't need any more wizard schools. Like the cleric they have enough love.
