It's been confirmed by the FIA that the pit straight is to be the location of the DRS zone in Malaysia. As long as you're within 1 second of the car in front 200 metres before the final corner you'll be able to deploy for the full length of the start finish straight.
As Webbo said:
"If it doesn't work here, I don't know where it will work,you've got a slow corner to open the lap, a slow corner at the end of the pit straight, and then Heathrow airport as well in terms of width, so it should work."
It makes sense that they don't allow it on the final straight, a point I made in a previous post.