There's some interesting news coming out about Saw IV, and straight from one of the creators Leigh Whannell.

According to a fan from the Monster Mania horror convention in the US this weekend, they heard directly from Whannell who talked about the film. The fan told Bloody Disgusting that the film is due to start production on April 16th, and they promised many twists and turns in this one as well as many unanswered questions from the third being addressed, particularly why Jigsaw poured wax over one of the tapes and the connection of Obi to Jigsaw.

Announcements on directors and cast will come, but as yet there's nothing other than the information above.

I would think that the film would have to address the issues left in the third film, they couldn't just leave them, and it wouldn't be a Saw film if it didn't have twists and turns, so there's not really anything new here, except...

We do get the strong indication that the fourth is a direct continuation of the third and that the work of Obi is not yet done.