The thing I'm worried about is the fact that they're saying this as if it is something to be hyped up and excited about.
Yes it is very nice to see Thief allow a no kill run. But the fact somebody had the need to come out and say this seems to imply that this person believed other people thought Thief wouldn't turn out this way, which is weird.
I understand that you killed people in the Thief games (The Trickster (maybe), Karras (sort of maybe, again), and Gamal (I guess, sort of maybe.)
Okay, so the above paragraph... structure. If it can be called that. Seems sort of weak. But what I want to say boils down to this: Why are they revealing this as if it is something new? Yes, I understand that mainstream games have all the killing in the world. But Thief was not expected to be a mainstream game. I don't know anybody that was worried about the Thief games forcing you to kill somebody and I don't understand why the developers felt the need to explicitly state that. Maybe they were just a little worried that people would think that Thief wasn't going very well and simply said that reassure people and it is as innocent as it sounds.
On the other hand, saying that Thief would have no killing sort of sounds like one of those scenes in a cartoon where a character says something like: "Yep, ABSOLUUUUUTELY nothing happening over here! The sink definitely did not explode!" And you can tell they're lying or hiding something.
So seeing the developers go: "Yep! Thief 4 totally allows a no kill playthrough!" I can't help but think: "WHAT DID YOU DOOOO?"