As much as I'm falling in love with Blades in the Dark, I'm still trying to what makes for an ideal setting for it, as I've had a few false starts bore hitting something that works with my current weird western.
Here's what I've figured out:
1) Systems of power rotten through with corruption and exploitation. The current order is a house of cards held up only by injustice, compromise, and brutality... and it responds with EVEN MORE BRUTALITY when it's threatened. People with power need to be desperate to hold onto it and so are more willing to take risks to hold onto it, which presents opportunities for the players (and other groups) to act when that deathgrip opens cracks in the facade.
2) A particular claustrophobia when it comes to the factions. everyone is in someone's pocket, owes a debt, or knows a guy. Can't swing a dead bluecoat without knocking against three different factions and at least two of them hate you. While this doesn't necessarily mean you need to have everything happening in one city things need to be close enough together that the crew is stepping on someone's toes no matter where they go. This keeps the crew playing the game of politics, trading favours for alliances while constantly risking the wrath of those higher than them.
3) Vice as societal lubricant. Just like the crew needs vice to unwind from their capers, the setting needs flow of vice to keep the wheels of power turning, no matter how greasy they get or who gets crushed underfoot. The masses need distraction, the elites need excess, the industries need fuel, and the strange need power. This gives the crew endless opportunities to find someone who's buying what they're selling, or piss someone off after their antics interrupt the flow of commerce.
4) Enough is NEVER enough. An organizing principle of any world using Blades as a system is that no one ever has enough of what they need, and so is driven to desperate action in order to get it. Even those on top of the pyramid lack the control they desire (see point 1), and everyone they squeeze to get it finds themselves grasping for something else too. NPCs who are rich in any one thing should be hungrily lacking in something else, be it material resources or ephemeral things like recognition or inner peace. When the debt comes due, the crew always owes more than they can pay off, meaning they must take further risks to try and stabilize, forcing them to bite off more then they can chew each time.
5) The Clock is Ticking. Whether or not they know it, every time the crew goes through the setup/mission/downtime cycle they're getting closer and closer to something big happening. One of the city's long standing tensions boils over into outright conflict, someone important dies and leaves a mess for others to clean up, something well and truly weird happens and it throws the system into chaos. Sometimes the party will kickstart this chain of events themselves, but it's always a good idea to have at least one in your back pocket, that way if they play things safe you can spring the unexpected on them and knock them out of their predictable pattern.
