About the Pact Boon question, if you've read En5ider you know there's potential there. I really like the "Pact of the Evil Eye" that was featured in En5ider #042 "Heroes of the Night" (October 2015) by Brandes Stoddard of Tribality.com and Harbinger of Doom Blog. Great example of a classic profane magic trope filling the right niche. I'm actually kind of surprised that WotC didn't think of the idea, given that they had a mid-4e Theme devoted to the concept (Oracle of the Evil Eye, "Character Themes: Born from the Feywild" by Logan Bonner, Dragon #405, November 2011).
I like the Hexblade Patron idea. It's a good way to model characters like InuYasha whose key character ability growth is through mastery of new techniques with a weapon. Could also model Frostmourne from Warcraft 3/World of Warcraft, for example. Arthas is a total slave to the blade, and the Lich-King behind it (while other Death Knights might be Blackguards ala the Paladin UA or perhaps Pact of the Undying Bladelocks).
I don't really understand the Shadow Hound feature, as it doesn't seem right for the theme – like it was jammed in there because it's a cool ability and they couldn't figure out who else to give it to. I also feel like the Raven Queen stuff should be contained in her own patronage section. I mean, yes, she's awesome and has been woefully underused this edition (as with much of 4e's flavorful materials), but she doesn't need two separate Warlock Pacts.
It's interesting because I always considered the Pact of the Blade the Hexblade chassis, with the Pact of the Chains a Binder chassis and Pact of the Tome a default Warlock Chassis. But here the Hexblade emerges as a more centralized weapon-themed subclass, showing that the subclasses really are the Patrons, even though the Pact Boons completely transform the class into a different beast. I think it would be pretty weird to play this subclass in the Pact of the Chains or Pact of the Tome, especially since you'd want to make your Hexblade a Pact Weapon so that you could take Thirsting Blade and get that extra attack. You're not playing your role as a melee-combatant if you don't have extra attack or some sort of sneak attack equivalent. But it's entirely possible to do Hexblade with a non-melee weapon (opening up that weird question again that Pact of the Blade has too – why is the word "blade" there if non-bladed weapons can be substituted in?). In addition, for Archfey Patrons (presumably those bound to the Maiden of the Moon, but the invocation doesn't specify it HAS to be her), you can now form a Pact Bow. This is a big step for Pact of the Blade enthusiasts, but is incompatible with Hexblade Patron. So if you want to go Hexbow for some reason, then there's your case for doing Pact of the Chains or Pact of the Tome. Of course, it's probably easier just to learn Eldritch Blast and use that to strike distant targets.
The more I think about it, the more the Hexblade could have the potential to model InuYasha's swiss-army-knife-sword the Tessaiga, and similar blooddrinking, ability-stealing weapons. It would be interesting to have some sort of hexblade-tied invocation that allows for special abilities like that weapon has – like breaking barriers, shooting out diamond storms, or creating tornadoes and blades of wind with its force of arms. There's so much potential for expanding Eldritch Invocations with homebrew without hurting the balance of the game, since Warlocks only get 8 in their lifetime, so Hexblade could be a root model for this sort of thing and then the DM could expand it for the sake of their player.
I just don't understand that Shadow Hound's role in this…
The Raven Queen pact is awesome. I never saw her as a Warlock Patron (she was a deity in 4e, and still is in the Nerathi Pantheon in 5e DMG), but boy does she fit. And the raven themed powers are awesome and exciting. Could easily be reskinned for entities like Odin, too.
Strange that they are playtesting expanded options for the Seeker Patron but not the Undying Patron or Undying Light Patron. Maybe there's a rights issue with the Sword Coast Adventurer's Guide? And maybe the Undying Light Patron didn't catch on? When they released "Light, Dark, Underdark!" SCAG had just come out, and I asked Mearls on twitter why they went with such a similar name, and he said that it was a miscommunication between the two teams. Made me think that when they license out to Green Ronin Publishing or whatnot, they're not as closely following their design work as they should be.
But Seeker was an odd patron, and odd that it got a Pact Boon all to itself. It seems weird to me that they're pushing it again here. I do like the multitude of new ideas of invocations specialized to different entities that might be your Patron. It's a cool way of customizing a subclass further and recalls to my mind the Sorcerer-King Patron in 4e's Dark Sun Campaign Guide, and how they later had a Dragon article providing customized options for each of the different Sorcerer-King's Templars (considered Warlocks in 4e, rather than a type of Cleric). In fact, that overlap between Warlocks and Clerics in Dark Sun may well be the same idea governing that followers of the Raven Queen are now Warlocks. Not bad, Wizards, not bad…
As for Wizard (CLASS)… I'm so glad they finally figured out a Generalist Wizard that doesn't (A) step on the toes of the Sorcerer, (B) step on the toes of the Specialist Wizards, and (C) feels like its own concept, rather than just "I'm a dabbler of different schools." This is a Savant, a master of knowledge and research, and is a major angle the Wizard was missing with all its specialists (and bladesingers and theurges). This is someone who has mastered the Spellbook and thus focuses on the versatility of the Wizard, rather than playing versatility like a Bard might or like a Sorcerer might. I especially like that they can turn Acid Arrow into Radiant Arrow or Finger of Death into Finger of Flames – but actually, even more potent than that is that they can target your weakest save (1/rest). I also like that they're intellectually aware and can get a jump start on the action because of their acuity of mind.