This initiative of Player Agency and Immersive Simulation is wonderful. Great sentiments to put at the forefront of your design philosophy! But they aren't really at the fore, are they? You want the player to be able to move and interact with the world on their own personal urgings, but you've scoffed at dialog trees and drastically underplayed the importance of verbal NPC interactions. These are as important to the simulation as anything else.
I get it, you don't want this to be Mass Effect. You want actions to speak louder than words. This is the Deus Ex way. But you mustn't hate words. I don't know about you, but when I'm involved in a conversation I need to be able to control my end of it. I need to have the freedom to chose how to express myself and opinions. Without it, there is no player agency; the social qualities of the character, the thing that makes them more than just a doll, is on rails. The exact thing you are trying to avoid is now a prominent blemish on an important facet of the game.
Granted, the men and woman at Arkane Studios have not out-and-out said there are no conversation trees. They mentioned there will be a few moments in the game where the player will need to make a choice in a dialog scene. But mostly they have kept very quiet on social interaction in-game... except to bash them in Mass Effect. This leads me to a measure of fear and loathing.
I have a hard time getting into games that don't let you play your role in the story portions, or exposition, but only when you need to kill things. My two favorite games are Deus Ex and Knights of the Old Republic. I see them as two sides of the same coin, each with their own strengths and weaknesses... some of them opposites. The only way to beat either of those games in my mind is to put them together; the player agency, immersive sim, and action-based decisions of DX, and the robust dialog trees of KotOR. Of course, both have great stories, rich atmospheres and solid RPG mechanics. Deus Ex has a broad social element, but the choices within the conversations are mostly an illusion.
Dishonored has the potential to succeed on all fronts, but only if the devs stop being so afraid of looking like Mass Effect. You won't look like Mass Effect if you do it better than them. But you will look like another tedious action game if you don't allow the player to participate in the story and conversations. You will never bore the player with this freedom if they can turn right around a stab the person they were just talking to.
-~::Pinky::~-