How about a Free For All "Vampire" mode... where shots you make give you points, but also take that many points away from whoever you hit (or maybe a percentage of the damage)? But don't take away that person's XP they made so far -- just the score. Was chatting with a couple people in the game plays a 6-player FFA and they thought it was a cool idea.
this would make deathmatch games last forever if you just kept on taking each others health away, it would end up you spent 3.5 hours on a a simple 3v3 team shot match, unless the teams were very uneven........still a good idea though, maybe you could just take half of the damage as health instead of all of it as health? that seems like it would be fun