Something I do with my players is allow them a number of NPCs that they can pull out at any given time. Say a player needs a to see a friend he knows of, so he just gives a description and brief backstory and I as the GM create the location where he can find them. Only rules I have most be a...
Also look at crazy history stories, examples: Shanghaied, press gangs, Edinburgh body snatchers, London undergrounds and such. The biggest thing in a city is figuring if something mundane or supernatural.
Got to say I think conditioning plays a very big role in this; size and shape of books are imprinted in us. When something is outside of those parameters it feels and looks wrong. (Okay, it may just me)
Well, back in the day it was a lot of history books about European history and design that I could steal and base my games on. :) You use what is most available to you. :)
I don't want the magical of fantastical to be placed into a game world just because it is cool. There need to be some thought to how it interacts. Magical and the fantastical should not be an answer but a resource in the game.
Personal taste, I like a world like Warhammer or The Witcher...
Thinking it is the other way, AI replacing Players. The GM would set the parameters for the AI to follow based on the campaign and let it run and just throw plot hooks and NPC in.
Warhammer and Earthdawn for me. Settings were fun.
I do enjoy The Witcher setting but not from the TTRPG but from the computer game, use the World Book that was published way before the TTRPG came out.