The first thing that come to my mind when I hear "Juggernaut mod" is: everyone play alien and one is promoted to human. Everyone try to kill the badass human with a Xeno Suit, Arcane Suit or whatever (really classy, say all black with bright blue accents or something), and that human has a really powerful gun. Every alien on the map should try to kill it.
The Alien that will give the final blow gets "upgraded" into a brand new human with an Arcane Suit; and the killing starts anew.
The first player to kill 20 or 50 aliens win.
Aliens do spawn around the map from eggs, and destroying an egg is equivalent to killing an alien that can move. Eggs sprout back after some time.
Now, that also works pretty well with an Alien instead