Given the all great reviews this game has been getting, would it be possible for the developers to see the interest in the game and release some form of mod tools?

It would be cool, but I wouldn't bet on it.

Making these huge levels is probably a very complex procedure and their tweaked Unreal editor might have a bunch of custom middlewares and stuff attached to it so they aren't allowed to release it without major changes. I don't really know this for sure though, just my speculation

But yeah, it would be cool if it happened. The Thief community done a lot of great large levels, and it would be neat if the same thing happened to Dishonored.

I'd like that. There were some GREAT fan-made missions for Thief. Including the awesome fan expansion to Thief 2 which
was absolutely incredible.

Yeah, I consider T2X to be the best mod fans ever created, to any game

The voice actress behind the main character used to be a regular here years ago, very nice person

That's why I love when games have modding capabilities. Lets you get so much more out of a game. It's a shame that Unreal Engine III games are so closed off to modding.