Looking at the art they have for the subclasses, I'm guessing the species are:
Reanimator Artificer: Human
College of Spirits Bard: Rock Gnome
Grave Domain Cleric: Dhampir
Hollow Warder Ranger: Storm Goliath
Phantom Rogue: Reborn
Shadow Sorcery Sorcerer: Hexblood
Undead Patron Warlock: Infernal...
Dagon was a Demon Lord in 3e and possibly before.
And Grazz't is allegedly the son of Nyarlathotep and Pale Night.
So some of them do have places in D&D outside their appearances in Deities & Demigods.
That's not counting the current PHB explicitly calling out Chthulhu as a potential patron...
There was a 2e fanon theory about Ravenloft being the Prison Demiplane that Tharizdun was imprisoned in. It would almost be like that.
And in 5e it's very possible that it could be a Domain of Dread too
Cure Wounds, Healing Word and Heal do not have the restriction about undead, I just looked at them in the PHB.
They brought up that point when they mentioned the Warlock could have a skeleton familiar, and that it could be healed by those spells.
I think they could bring back Epic Destinies too as something that 4e had, though no one will probably use them. They'd just be feat chains of Epic Boons.
I think these feat path ideas might be a good thing to go with certain species, though I guess they probably won't try to enforce species requirements for something like a Path of the Fiend or Path of the Dragon, even if they might go very well with being a Tiefling or Dragonborn respectively.
I think Conjurers can be spooky based on the fact they can summon some terrifying things like Fiends and Aberrations.
Diviners can be spooky just by knowing things they aren't supposed to know.
Enchanters can turn others against you, so that's scary.
You could argue that Necromancers are among the spookiest Wizard subclasses, but with some work so can most other Wizards can be spooky with the right character and concept.
Yes even Illusionists.
But which ones requires the most work to be spooky?
I think it's the Abjurer, but anyone else...
I find the wording about Infernal Wound dice to be confusing, why ever say you get 1 dice when you get more uses.
I like the Druid, but I want the damage of their attacks to go up with size increases. Yes I know they're adding extra damage from their Druid abilities already and get 2 attacks...
The novel The City And The City could almost be Urban Fantasy, as there was certainly this idea of a veil and an "unseen world", but it didn't quite have magic in it like many of China Mieville's other novels.
As for a new setting, I think the days of having new expansive, excessively detailed...
I think single class Monk that uses an attack action and then uses flurry to attack more is probably the better thing most of the time as they get 5 attacks.
Maybe if they got the ability to use a cantrip such as through species like Tiefling, then it might be better just using attack + flurry...