Sorry to take so long to reply....I had a busy weekend.
No worries.
I think the bit I quoted here is really just about preference. I know based on our past discussions that you prefer to play with the expectation that the PCs are "no one special", they're just another person in their world. Which is fine, of course. I don't really care to try and hew to some kind of quasi-medieval social class expectations; my players come up with characters they want to play, and I work with them to make that happen. Any advantage they get from their background is easily offset with an equal disadvantage.
As long as you're applying disadvantages to cancel off advantages I'd likely have no problem with it were I in your game.
I also think that the life of an adventurer is simply different from whatever society woudl consider "normal", so to me, PCs are special no matter what. They don't need to be some kind of "chosen one" or anything, but I don't think that they are typical by any means.
But again, this is simply preference.
I tend to prefer the zero-to-hero arc, particularly as it helps allow for some long-term growth and change during a long campaign.
Aren't many of the choices made by players for their characters made to gain an advantage? Weapon or ability selection, spell choice, feats versus stat increses, what magic item to wear in their belt slot.....all these things are done with advantage in mind. There may be other factors as well, but mechanical advantage is likely always a consideration.
Indeed, but in my game almost all of that happens at char-gen which to me largely falls in the meta realm anyway. The magic item one - that's almost always explainable in the fiction through the PC's own sense of self-preservation.
Why is that a problem in the scenario you describe? I will point out I think it's a bit of an extreme, and certainly different than the one I presented in a couple of key ways, but still it may be interesting to discuss. What's the big deal if the player does decide to claim lordship of Karsos? Sure, it may make things easier for them in the immediate "hey the guards aren't gonna kill us" kind of way, but I woudl also think it would open up several opportunities. What's the PC's place in Korsos? Are people happy for him to turn back up? Was his family glad he was gone? All kinds of political angles seem to present themselves.
Two problems leap to mind.
One, if player A claims lordship of Karsos it denies players B, C and D the option of doing so should they have so desired.
Two, it grants potential advantages (wealth, status, authority) that wouldn't otherwise be present; and while some of that can be cancelled out by political considerations etc., to do so presents a here-and-now headache for the DM which could have been thought out earlier had this fact of nobility been known earlier e.g. at char-gen.
Now, if the goal of play is not to get embroiled in the political situation in Karsos, these concerns don't need to be raised. Perhaps something else can be done with this bit of info. But the question is if this isn't the goal....if this isn't what the player wants, then why would they introduce this idea? Just to avoid being bothered by some guards in a potentially hostile town? Seems a bit of a big card to play for that reason.
It comes under the aegis of player advocacy for their PC, and looking for an advantage.
Does this interfere with the DM's plans? Or the other players? If so, can that be reconciled? I would imagine a conversation would happen, and the best way to proceed would be decided on by all.
Well for one thing if it did interfere with my plans the last thing I'm going to want to do is tell them that!

That said, again if I-as-DM had known earlier about this nobility bit then I could have planned around it and even incorporated it in somewhere else if it made sense in the fiction. (e.g. the PC would likely have been dealt with much differently in some towns previously visited, and approached said visits differently also, had the nobility piece been known up front)
Again, I don't see the problem with the stakes. To me, it's the idea of the player's background actually becoming important in play. That means the player will likely be more invested because the character is more tied to things.
Yes, which means let's get the important bits of the background known up front rather than appearing out of nowhere halfway through.
I can't make something important in play if I don't know it exists.
As for the "slippery slope" kind of argument....I don't think that's really a concern. Perhaps with certain players or certain groups, but I think that in general most players can actually handle this without abusing it. It may take a little adjustment to actually incorporate this kind of thing into a game where it previously didn't exist, but I think it's achievable.
For me it's a very great concern.
Well, in the case of a wizard or cleric, I don't know. In my 5E game, one of the characters is a Diviner. She gets those kinds of hunches all the time. Perfectly within the fiction that's been established.
Fair enough.
And I'm sure we could come up with an explanation for just about any scenario.
The easiest would be to not confirm that the PC is actually dead. Just cut away leaving her actual status unknown. Maybe she's in negative HP, or making death saves or whatever. Then you'll actually get honest action from the players. This would probably be ideal if you want to avoid metagaming.
The way to achieve this (and how I do it, when I can) is to take the scout's player aside and sort the scouting out beyond the hearing/knowledge of the other players, then leave the scout's player aside while I deal with the rest of 'em.
Don't you just flash forward past the hour of waiting? I would expect so. "Okay, an hour's passed and the scout has not returned....you all have an uneasy feeling about this," and you're all set. Play proceeds largely as it would have without the need for pretending not to know what we know thing. The players can play their characters without their knowledge of the scout's death impacting their decision making.
Sometimes yes, other times something might happen during that hour e.g. the main party are forced to move and thus won't be there for the scout to find on her return. Or, if the scout doesn't return after an hour and they really don't know why, for all I know they might say "Let's give her another half-hour"; an outcome much less likely if they-as-players already know she ain't coming back at all.
