The trailer was officially released 4/1/13. I'm hoping it's an April Fool's joke. Otherwise it's like replacing Darth Vader's voice with Bieber's. Ugh.
Heh. After venting over on the official forums, I hope you're right and I get to feel foolish. I was never one who thought Thief 4 had to have Garrett, but if it does, I really think it needs to be Stephen Russell.
Join the Kickstarter for Torment: Tides of Numenera, the successor to Planescape: Torment: http://www.kickstarter.com/projects/inxile/torment-tides-of-numenera