So I'm asking myself, why all the secrecy regarding NT1? If it's just Reach's Firefight mode, why not just give us Firefight? Drop a few waves of Elites in there, and bam. Nothing we haven't played before. Why make it Spartans vs Elites? Why is the goal of the gametype so simple? Why use the co-op netcode for this at all?
Spasm's greater NT1 theory:
NT1 is actually Reach's special blend of 3 herbs and spices; Campaign, Firefight, and Adversarial mode.
3 Spartans vs 3 Elites, with both human and Covenant AI soldiers scattered throughout, for the entirety of the regular campaign.
For the Spartans, it's pretty much business as usual. Play through the story, clear out skirmishes, and keep trying to advance to the next checkpoint. In your way this time though, are 3 Elite heroes controlled by other players.
The possibilities for the Elite player logistics would be numerous.
These Elite heroes could spawn in squads of AI Grunts as captains. They might even be able direct them in battle (remember the regroup command on the Controller layouts?).
They could possibly earn better squads (Jackals, Hunters) through performance/checkpoints.
The number and type of squad AIs you spawn could be a loadout option.
Seeing as how the emphasis should still be on progressing through the campaign, Elites could have one life, and be forced to spectate till the next checkpoint/skirmish, or keep spawning as long as they still have AI squads alive. Hell, maybe there's even a plot point in the campaign where the Elites are supposed to be victorious, and these rolls are reversed.
...Or it could be regular assed ol' Firefight... I guess...