Eh... yes and no.
I would like it to go in the dark and mature direction, but that means being actually dark and mature - not dark and rather juvenile.
The Meat King's party was kind of a mix. The idea of a BDSM party in an abatoir was very imaginative and parts of it were really atmospheric - however the actual people attending the party were rather disappointing in that it was big guys in gimp masks and skinny women in fetish stripper outfits. I'll give it some leeway due to technical constraints and being smashed out in a hurry - but honestly once you arrived at the party proper for me it stopped being dark and started feeling like it was designed by a socially repressed teenager who knows about BDSM from stealing his big sister's Cosmo magazines.
Dexter Industries, The Saints, Dom's Strip Club, etc were supposed to be dark but largely subverted a lot of the game due to the ridiculous, over the top nature. It's not so exciting to be a Hitman who can kill anyone and remain undiscovered in a world where you can blow up hotels, run snuff movie studios and perform incredibly cruel experiments in plain sight and remain undiscovered. It's also harder to take settings and enemies seriously when clearly a top priority was "how can we fit as many sexy women as we can in here".
Dark places are most horrifying to us when they can exist in the shadows of our own world. I'd like to see them take more inspiration from things like A Vintage Year/The Lee Hong Assassination, where criminals hide their lairs over credible businesses and build upon that. As well as helping with the "start in a safe area and move into danger to reach the target" approach of level design, it helps build horror if you don't know what you'll discover until you set foot inside.
I'm a grown up, if I want to see boobs I can go to a strip club. So I think that sexy women should be used strategically - there's undeniably a trend of male crime bosses to want sexy women for their own comfort, but there should also be focus on these guys as being efficient and disciplined. These are supposed to be targets who warrant the attention of the finest assassin who has ever lived, not Tony Soprano's drinking buddies.
Due to them handling them poorly in the previous games, and that the market is over saturated with people using them as a shorthand, I'd like Hitman to steer away from "dark" topics like coerced prostitution and crack houses, and branch out into alternative great evils like:
- Organ harvesting/red market (possibly hidden in a free clinic or such)
- Market fixing/Industrial sabotage (ala Le Chiffre's original plan in Casino Royale - short stock and then blow up a business, or maybe just abduct and torture people for company secrets)
- High end money laundering (something like the Firm, a law firm that kills off employees, takes prisoners, tortures, etc)
- Forced labor/slavery (sweat shops producing anything from clothes to weapons)
All of these things allow for the veneer of respectability and the descent into things that are really dark and horrible without going all cartoony evil, thus keeping the maturity.