My initial impression was 'why wouldn't you make the movie to coincide with Halo 3, the 'completion of the story arc'... But maybe that wasn't enough time to make a quality movie. I mean they would have had to make the movie faster than they made the game...which just doesn't seem possible.
Now, I'm thinking, 'if I were a Movie exec. or even a Microsoft exec, and I couldn't get the movie done for the completion of the 'story arc' presented in the videogames, when would I want the movie to be made?'
What if the reason they have backed off of this is that they would rather make the Halo movie AFTER all the Halo games have been done? Like the punctuation mark for the franchise? Go out with a bang, as they say... There would be no game sales to ruin if the movie wasn't recieved well..
I think theres still hope that this will get made, even if things look gloomy right now. It makes more sense to do it after the games have been completed, because by then your target market is at its highest. Just look at how many more people got into Halo AFTER Halo 2 was released...It'll be the same for Halo 3. Also Bungie would be able to be more involved if they weren't simultaneously working on the most important game in the franchise.
I think the contract will get picked up, and production will resume very soon after Halo 3 is released. Like you have all said... it's guaranteed to be a hit.
So, theres something to think about and hope for...