Console games can barely handle 32 player servers. We're going to see that new stupidly named "Massive Action Game" on the PS3 try to do 100 players but we'll see if that actually pans out.
The big problem is communication. Even with 24 players, DICE couldn't figure out how to do team wide communication in Battlefield Bad Company because of lag. And even if they could work it out, imagine 99 other Halo 3 players in a single room. It would be a chorus of 13 year olds calling you a nigger or a fag. Fun times.