Via HaloWaypoint:

The Halo 4 and Team Hardcore playlists are now available in Matchmaking.

Team Hardcore currently includes Halo 2 Classic game types. Halo 3 tournament-approved game types will be integrated in a future update.

Other fan favorite playlists are also in the works, including Team Snipers, Team Doubles, an objective-only playlist, and more – stay tuned for details regarding when these will become available as featured playlists.

As always, playlists data and feedback will determine which playlists become permanent additions to the playlist lineup.