Some interesting thoughts in here...some I agree with...
Next: I think there's a good chance we'll see "Mystic #3" next. That's where it falls in the alphabetical order. They clearly want to get a psychic class introduced into the game. It would be nice if they put out something in UA that was complete and thorough and, well, tested and vetted for flavor and crunch with a sufficient number of subclasses to give [most] psychic fans what they're looking for all at once.
Then, I reeeally wouldn't mind, to be honest, if they SKIPPED Ranger altogether. We have two different "base" rangers. We have, what at this point, a half dozen or so subclass options. They've already done 3 UA's on the Ranger. ENOUGH already!
Rogue: I'd love to see how they'd do a committed Acrobat subclass, but I doubt it would happen. I'm kind of at a loss for other Roguish optinos. A "divine 1/3rd caster" equivalent to the Arcane Trickster would be expected. Whether that's Inquisitor" or Avenger or "Assassin's Creed" in flavor/slant I can not say. An Artificer might be an interesting [for those who like artificers/eberron] twist, and alternate type/example of "magic rogue" for those who aren't interested in being a "trickster."
Sorcerer: I've done several iterations of sorcerer subclasses. To reiterate, sorcerer's are broken into the "Ancestry" camp: Dragon, Favored Soul [celestial], possibly Storm [if you use an air elemental or djinn as your back-/origin-story] or "Environmental" camp: Wild Magic, Shadow, possibly Storm [if you're not using an ancestor origin/backstory]. That in mind, they seem much more interested in working the "environmental" angle so that those involving other beings are more focused on warlocks. I could see/and would make sense, to include a Fae origin. An Elemental origin, since like Storm, you could worked that as either "my great grandmama was a X" or "you fell into/slept near/woke up in/whatever a font/vat/portal/whatever of elemental power." Might see a Duskblade. Maybe a Soulknife [especially if they bring Mystic in, they can start intro-ing psychic-base/-flavored subclasses for other classes]. Not that I care for either. But they're a possibility. The sorcerer has a lot of untapped potential.
Warlock: Sha'ir [genie based pact]: creates a pact for a genie-servant who grants spells-casting ability other warlocks don't get. "Binder/Diabolist": a warlock that uses and gains multiple/different pacts -mostly temporary, maybe some permanent- with different entities to get things done/increase their power. Also, multiple [at least two] new pact options and a few invocations. EDIT: Oh! and I forgot. I would like to see, though I don't know what you'd call it, a Celestial Patron warlock [and probably accompanying additional pact and some new invocations]. /Edit.
Wizard: Tradition of the Craft [folk/nature magic/traditional Witch], Tradition of the Magi [generalist mage]. A Runecastersubclass [versus the "prestige class" model they've already presented] to dovetail/follow the giant AP makes sense also. Alternately, for Wizards, since they already have so many existing subclasses, they could just present multiple different 5 level "prestige class" traditions to provide an additional "layer" over the existing schools. So, as the runecaster we already have, you'd have a "Generalist/Mage" prestige class that just lets you pick some other schools' special abilities as you advance, maybe gives you a magic enhanced strike with a special staff. A Shadowcaster [like a rune caster but shadowy powers]. Not sure how you'd do a witch this way, but it probably would work. etc...
That's mostly my thoughts.
I would think, after the subclasses UAs I think we'll see a return to setting-specific material. For example, a special race or subrace, couple of subclasses, couple of backgrounds, maybe a [very] setting specific feat or languages or some kind of flavor material for a giveen campiagn setting.
