I don’t know if it is true but on a Bungie forum the other day some people were talking about how Bungie have hid something in halo reach that is huge! a very bid deal, and they said it will be harder than the IWHBYD skull in halo 3 to find. (the only reason people found this skull was because it was leaked.)
Just like the ‘Secret of Sandtrap’, it was never found, if Bungie have hidden something HUGE, they would have gave us huge hints before they gave full control to 343i.
I think the biggest secret is that there are no more secrets, just the rumor of them. The rumor of a secret costs nothing to create, but creates a lot of interest in the game and gets some people to play more, searching for things that don’t exist. It only ends up benefiting them in the end, and it costs them nothing to do. The secret of sandtrap, the assassin skull… just look through the old H3 forums. Same has happened in Reach. In the end, nothing will be found.
Maybe the tribute room was the huge secret.