i went and listened to the bungie podcast that they put out since it was entirely about forge, http://www.bungie.net/News/content.aspx?type=topnews&cid=12734, and they said (i`m responding to gremlin here) that even game variants technically work different now...that matchmaking has both a game variant and a map variant attached to it...so that player creations (i.e. mlg possibly) could be implemented in matchmaking and, from the way they sounded, fairly easily. so hopefully (though i bet doubtfully) there can be a constantly evolving mlg playlist in the future.
Best part is how you get represented by a monitor. Thats insane I always liked that idea I figured it would be just for specating in games but to be in forge and you can actually die is insane!