There have been many people who have complained that 4e is too much like World of Warcraft. I say, take a few more ideas from it.
I can see many options for this, one on one, free-for-alls. team battles, and multi-team battles. See who can build the best character and play it best, see which team works together the best, or just get a buch of people together to kill each other.
Why would a 6 person team be able to take down a mighty dragon?
It would definitely be tricky to pull off, but to have a large group play through a dungeon might be fun. The dungeon, and possibly the enemies, would have to be modified to make it accessible to a larger group.
It might work where there is one DM in charge of a certain amount of players and they each group take their turns at the same time, when everyone is done with a round, then the GMs start working on the monsters.
Well, I don't know if they would work, but I think it would be interesting to try. I'm going to try to convince my gaming group to try some PVP (shouldn't be hard) and depending on how it turns out, I'll try to post about it.