This is a very good thing. Arndt is a deft writer with an outstanding grasp of structure and cinematic storytelling techniques.
Heat Vision report that Arndt is making a deal that will see him taking over from Simon Beaufoy.
The downside? That the film's schedule is pretty much set in stone. Arndt is going to have to complete his do-over in time for production to start in the fall. Here's hoping he's got the time and permission to do as much as he feels necessary.
Of course, director Francis Lawrence doesn't just have the existing script but also Suzanne Collins' original novel to draw on during pre-production, and much of the work will likely be deeply rooted in what Gary Ross established in the first film. This could buy Arndt a couple of months.