Might be announced at CES in January
While Bungie and Microsoft are already denying it, apparently there are some screenshots circulating that show Halo: Reach with 1,250 possible achievement points, which suggests that new downloadable content is coming that includes 10 new achievements.
According to a number of sources, some DLC is planned for Halo: Reach, which is no surprise. At least for the time being no one is talking about it, but we suspect that it is in development.
The big question is when might Bungie and Microsoft be planning for this DLC pack to be released? We suspect that with more DLC coming out soon after release, a release before the end of the year is possible; but we suggest early next year might be a little more likely, after talking with a shadow dweller who says that they will want to sell as much Halo: Reach this holiday season as they can before dropping the DLC.
The best guess is that Microsoft will announce the Halo: Reach DLC add-on during CES in January.