I'd like to say that I want the magical stuff gone, but the best parts I remember from my playthrough of Thief were the magical parts and strange locations and levels. Toned down, this game looks a lot like Dishonored, mildly mystical Victorian thieving. At least we know Garrett is not an assassin, but I shall eat hats if at some point in the game, particularly towards the end, Garrett is not required to murder someone.
Focus sounds a lot like Batvision from the Arkham games, or the other 'special vision' thingies. It doesn't look mandatory, so far at least, and is likely just to help visual identification. Unlike the good ol' days of 1999, there is a lot of visual density in modern games and it isn't always obvious what is usable and what isn't. Think the highlighting thing in Deus Ex: Human Revolution that you could turn off. It also reminds me of that ability in Dishonored where you can sense extra stuff around you.