It would be pretty simple. See L4D did the same thing. L4D had matchmaking for Campaign, Versus, AND Survival. Ive played the PC and Xbox version, sadly everyone talks and works as a team on the PC. And guess what, L4D Versus IS Campaign, its just that some people are controlling the zombies. And on top of that it had a vote system where you could change map, difficulty, and vote to kick undesired players. Valve has always been better that Bungie, but this shows that Bungie isn't willing to implement things that work for other developers. Honestly, those who want to play with friends have nothing to lose, they don't HAVE to play with randoms, its an option. Because their are some of us who don't have friends on Xbox Live.
And on XBox Live, you aren't going to find anyone that will stay connected for the whole game, thus ending the fun for everyone.
Frustration will be at an all time high...
If dumbass bungie would of implemented host migration and in-game join, that would not be a problem. L4D does it and does it well. I guess its one of the reasons why it got GOTY
[Edited on 09.23.2009 7:37 AM PDT]