Since a lot of the UA's seem to be asking pretty big questions about the classes/the game (evil PC options, built in fluff for fighter subclasses, guns), it seems likely that the sorcerer will ask the big question of more monstrous? I think we will see a more transformative sorcerer--something like a revised favored soul (makes you more angel-like), a fiend bloodline (makes you more like a devil or demon), tentacle bloodline...er, I mean the aberration bloodline, or a fey bloodline so your sorcerer can be like a sprite by level 20. If people curse that in the survey, we will get more things like the chaos or storm sorcerer.
It seems like there is are a couple more patron types for the warlock that could be explored (elemental, dragon, celestial?). The celestial seems like the most "big question", we don't have a lot of "good assumed" classes/subclasses (maybe the PHB paladins), but a scenario where the celestial wouldn't just gift the high Cha future PC with favored soul sorcery or paladinhood instead of warlockhood escapes me.
Before the weekly UA's I would have said "if you want to be related to a fiend, be a warlock, and if you want to get power from a dragon, be a sorcerer", but the UA's have been mixing themes around.
It is hard to say what you could do with a wizard that you can't do already with existing subclasses, so maybe the wizard will get tagged on to the warlock like the rogue to the ranger.
I assume the mystic will be after the wizard.