I don't want Halo to support that many players, at least not in ranked. With all the vehicles and things going on it would be a huge mess just like all the other games that support that many players. I like the fact that in smaller matches (4v4) every encounter you have turns into a personal little fight between you and the other people. It's like you have to earn every kill you get.
In games like KZ2 you kill so many people so fast that it doesn't even matter. It ends up feeling like some shooting gallery. MW2 feels the same but for different reason (lower health, faster action). 16 player matches are ok for Halo and if they have 24 player Social matches I guess it would be ok, but honestly Halo 3 Big Team Matches can be really laggy and chaotic to the point that it doesn't make any sense. I don't see Bungie using dedicated servers so anything over 16 would probably be a mess.