I've played more than a few hours into the game and I came up with a few ideas.
Your actions make a difference
I understand procedural generation is the whole genre, but what do you think about a permanent resource management?
one way to clear each map would be to fuck every monster; say there are 100 monsters, so 20 spawn in each map. if you fuck ten then there'll be 90 left so next map spawns 18. A way perverts can win by fucking the world to death
How about limited weapons and ammo? For melee weapons it'd force players to commit to moving forward or taking the time and energy to purify every monster they kill. Finite ammo means you can't just spray and pray, even when you have firepower you'll still need to use it wisely.
I understand the whole infinite money to buy infinite equipment but how about stats act as experience instead? You gain more health the more you're hit, more stamina the more you run, rename lust to libido and increase it by fucking, etc.
Differences in monsters
She butcher is already a damage sponge but you could have her call out to others when she's alerted and have her drop her weapon or health-restoring meat or something to balance her. Since you have a sack on her head you could make red spots on the ears to show she's deaf to remove sound-based detection.
Miss eye-in-mouth has only one eye, that could be an excuse to mess with depth perception, especially in melee combat.
twin-pair-legs has no eyes or ears so that means no sight or sound detection. You could give her a proximity awareness with the player character's footsteps.
Different sex positions for where you face the monster would give a nice variety especially if you're going to reuse monsters for different areas, there are for the weeping angel statues.
Punish rushing players
If you want to be an asshole you can also add spike traps inside chests to punish people who open chests as they're running away
give a reason to 100% every map, some reason to not just stock up on injections then run from entrance to exit, especially since obsidion keys can be bought for cheap. Maybe a counter of rooms explored that could give new dialogue and bonuses to Savina.
Sanity
Maybe not implemented yet but you could play with enemy shadows and the sanity meter.
You could take the Bloodborne route and completely overhaul the sanity mechanic, adding potions that reduce sanity and having invisible enemies, traps, or chests that only appear at a certain sanity level
