There’s already plenty of discussion on the github about a ‘faction’ mode that is likely more in line with this desire, as your faction base is supposed to draw attention, and danger can be significantly ramped up as the player is no longer limited to a single permadeath character. Part of this project includes improvements to NPC’s for defensive purposes, and the various options for attackers. Its definitely a longer term project, and hasn’t seen much attention in a while though. It seems like the initiative might have shifted to ‘proving’ it out so to speak in a rebuild of Defense Mode first. Both rely on finishing the decoupling of ‘player’ from ‘single character’ and improving NPC’s to be less dumb, and AI work is a particularly difficult, finicky, and thankless space when you want to move past the most basic of behaviors.
In the short term, have you tried playing with wandering hordes enabled? They’re not down to systemic scheduled attacks, but they are large groups that’ll converge on you if your doing loud shit, or just pass through if you’re unlucky… Been a while since I played with them myself to be honest so I’m not sure how much development they’ve gotten.