Yes, I am genuinely confused on this point. I am not trying to get you to change your game, I am not understanding how your game functions. Why would you address something that isn't a problem, because in theory there is a tiny little minuscule chance it could become a problem some day? Isn't there some basic threshold where it's not worth addressing at all, and wouldn't that threshold at least include "things which I don't already think are on their face ridiculous"? None of this impacts your world from what I can tell.
Okay then. To answer your question, the world is a sandbox and exists semi-independent of play. Some content gets introduced during play, as needed, but not necessarily onscreen, and at any given moment things are happening offscreen which may or may not eventually intersect with what the PCs are currently doing onscreen. This provides a living world for the players to maximize their scope for agency; it makes it easy for me to improvise events and plots and enemies because there's a premade context; it ensures a game that is more exploration-based than combat-based; and it scratches my simulationist itch in a way similar to game design or writing SF.
In short, it does all the usual things that a sandbox does. I wouldn't want to run a campaign setting that didn't exist until the PCs were onscreen in the game. Some lazy eval is fine, but all lazy eval is way too gamist for my taste and leads to retcons like "now that you're abusing Simulacrum I'll make all the enemy wizards have been abusing it for centuries too." Blech. That's way too late to preserve player agency. Better to create the world in advance.
Yes, I understood all that. I have no idea why any of that is relevant to my question.
I will ask it again, with emphasis added, "Why would you address something that isn't a problem, because in theory there is a tiny little minuscule chance it could become a problem some day? Isn't there some basic threshold where it's not worth addressing at all, and wouldn't that threshold at least include "things which I don't already think are on their face ridiculous"? None of this impacts your world from what I can tell."
Because the question you asked was "doesn't the world only exist when it actually comes up at the table?" Hence my confusion at your seeming incomprehension.
See again post #23, and I reiterate that your definition of problem is different in scope than mine. It is already a problem in my world, and it will become a bigger problem the instant a player asks, "How does that work? Why does it only work on hostiles?" You seem to think that it only becomes a problem when it affects game balance, but I don't care about game balance. To me it's a problem if it doesn't cohere, because running a coherent world is MY JOB as DM.
If that doesn't make sense to you, reread the thread. I've answered your questions multiple times. It's cool if you just don't "get" simulationism, but maybe asking the same questions over and over isn't going to get you any closer. Feel free to ask a new, different question though.
Assuming we agree, and since you previously said your players will never attempt something ridiculous like declaring their allies as hostile to game some benefit from a feat, that would mean that aspect of the feat never needs to be worked out by you - it's the worm. It's an minor aspect of the world that never needs to be worked out in advance, because it's not in advance of anything - nobody will care about the worm, or some silly interpretation of a feat.
Which comes down to the actual likely questions your players will ask - why does it only work on hostile creatures? So you can't think of a coherent reason why the feat only impacts people hostile to you? Is that really why you want to "fix" it, because you are having trouble coming up with a justification for why it only impacts hostiles? If so, it's likely a recurring problem, as it's the same issue inherent with opportunity attacks and several other mechanics in the game. I'd think it would be a lot easier, and more interesting, to come up with such a reason for your world rather than just change this mechanic to avoid inventing the reason on this rule (only to face the question again on other similar rules). Do you disagree?
Perhaps he's making sure that NPCs can't take advantage of the perceived loophole. They may be less trustworthy than his players.
It's not about trust - that interpretation of the feat is silly on it's face. He used the word ridiculous as well. We all agree the feat doesn't function that way. Much like his NPCs are not taking opportunity actions on their allies turns as their allies run past them because they are thinking of their allies as hostile to gain a reaction action. We all know what hostile means in this context, and it doesn't include your allies.
It is already a problem in my world, and it will become a bigger problem the instant a player asks, "How does that work? Why does it only work on hostiles?"