All of which is exactly the sort of thing I mean when you need to stop thinking of infiltrators as ninjas.
Right now, as it stands, infiltrators
are ninjas. I'd love for that to change but, as of now, they're ninja-nobles.
To me, it seems like you and Vellos aren't asking for more plausible deniability: you're asking for implausible deniability.
No, I'm arguing for ambiguity. For the same reasons players can't just go look up the battle code, for example, or fame points. Players should have a good idea of how they can protect their character and investments, because the game isn't fun if you can randomly just lose everything.
But players absolutely should not have a perfect knowledge of what is possible. IMHO, metagaming isn't a yes/no proposition: some things are more meta-gamish than others. And the very definition of meta-gaming is stepping outside the game; taking knowledge you know from beyond the game parameters (i.e. you know that peasants CAN'T attack nobles, which your character doesn't know) and applying it to the game.
As I see it, you're arguing that our characters live in a world where the game mechanics are their fundamental reality: that nobody had religions until religion was implemented, nobody ate food until food was implemented, the planet had no seasons until seasons were implemented, the manner in which food is consumed has been revolutionized several times, etc. You're making an argument which, to me, is as fallacious as the old High Tech Battlemaster joke page.
The mechanics are best-attempt proxies for the world our characters live in. And sometimes, the mechanics are insufficient guides, or incoherent guides, or contradictory guides, or even broken guides in the case of bugs. And when those things happen, you find a way to fix it with RP. And where the game, players, or some mixture of those two becomes complicated, confusing, "nefarious," the leeway for RP can, does, and should expand.
You don't really think every infiltrator always assassinates at night, in bed, with a poisoned dagger, do you?