This post is generally aimed at Frogy seeing as he manages all of the events - but it'd be great to get everyone else's input as well. Modify the idea a bit, make it better.
So, the initial idea is based off Battlefield in which how ever many people go out onto a battlefield and fight till the death - but it's a whole hardcore thing. If you die, you die - no re-spawning. The battlefield would be a 150x150 block map including bunkers, hills, tree's, etc, but you could modify the map to have multiple different one's rather than the single one, which could get quite boring.
I suppose teaming could work by going through one of two (or more) portals to choose your team. It's just a suggestion and a really basic idea at the moment, but I think it'd be quite fun. And if the Multiverse plugin was used, I'm pretty sure we could change the player's inventory to something else so they can't sneak their own weapons in?
But yeah, it's just a suggestion. As to whether it'll be used or not, that's entirely up to Frogy!