Someone made a thread about gaining perks from challenges, and it kinda got me thinking there was a possible opportunity, not necessarily for stuff like perks/uniques, but for at most a new central npc, or at least a bounty board in each town with room for rewards, and if a npc, possible room for a hunter with a bestiary of all enemies you've sensed/defeated, possibly separated into categories for less clutter like humanoids, constructs, ethereals.
For example, whether a npc is made with contracts, or each town has a bounty board, you can get new quests for specific targets. Not necessarily unique individuals with scenes etc, but unique threats. Stuff like say, wolves that have become tainted and extremely powerful, or possibly normal encounters with a gimmick that make them much more interesting/deadly. It gives room for more content and the ability to push difficulty to the limits without needing as much amounts of writing, while being optional. So people could have the option of either grinding weaker, normal area encounters, or going after the big targets, or both for completionists. It also leaves room for optional "superbosses", or stuff like say, Kass disguising herself as a odd looking common enemy, being a really difficult fight, then having a few lines of dialogue and fleeing.
If a npc isn't a option, then near the middle of each settlement you could have a board where you have a small wanted description, then in a set square on the map the board is for, you can trigger the encounter, once it's done, you head back to the board and receive your reward. Possibly get "bounty hunter" as a title for completing a majority or all of them. I know generally swiggity swoogity is the focus but I feel something like that could help make regions feel more "alive" and like you were helping keep the peace, and also for people who enjoy the combat. At the same time, the rewards could stay like hefty amounts of money, or just rare-ish items as rewards, so people who don't care much for the combat or don't want harder encounters can avoid it no problem.