Bungie has now announced that Halo: Reach will be gaining some interesting updates in the near future.
First, on October 19, campaign matchmaking playlists will be implemented.
Secondly, the rank cap will now be increased. Any credits earned beyond Lt. Col. Grade C will now count towards a new level whenever it's added which also means any players to get this far will have access to some new stuff. The update for this is not set in stone however Bungie.net says it should be within the near future.
If you need any more information on this update head on over to the Bungie.net blog.