Some things posted on Bungies developer blog and weekly update are teasing that something crazy is going to be in Halo Reach. Here is what was posted so you can see it for yourself.
Steve Cotton is working on one of the craziest things ever in a Halo game,(As shown in the title.)
What Cotton is playing around with right now is beautiful and alien and huge,
Brian launched into a bevy of questions designed to break Cotton down and reveal all the holes and limitations in his master plan, but at each and every step, his efforts were easily foiled by Cotton's expertly crafted construct.
We joked that what Cotton's working on deserves a ViDoc all by itself, and as we walked away, Brian and I realized that the sentiment really was no joke, it said. We really could drop ten minutes covering just this. Easily. But then again, I could drop a single image and it would probably be enough to send you over the edge.