Those Halo wheels are still turning. And from what a Gamasutra job announcement seems to hit at, Peter Jackson's Halo game is moving forward. The Microsoft Game Studios job listing is for "Creative Director - building a new Halo universe" and says this under responsibilities:
Direct the tone and timber of the project with an eye towards compelling character development, visionary narrative progression, and addictive gameplay
Partner with key Hollywood talent to collaboratively craft a masterful game experience
Bridge the gap between storytelling and the interactive experience while delivering on the Halo soul.
Collaborate with game play designers, story writers, game writers, and said external luminary to deliver on a unique game in the Halo universe...
So that might be Peter Jackson — unless Microsoft has roped in other "key Hollywood talent" and not told anyone. Microsoft's been pretty bad about not telling us what's going on with the new Halo games.