My vision of a new 4 kings are 4 that specialize in a specific area. They would retain the massive HP amount and re spawning capabilities if you took too long to down each one.
I imagine a Flame King...he would be impervious to fire (like Quelaag) but wield incredible fire techniques exclusively.
I think of a Magic King, who used catalysts of epic proportions to cast powerful sorceries as well as ultra high defenses to magic.
A 3rd King of Lightning would be present. Gwynn would be a puppy compared to this dog. Uses Zeus like thunder and high resistance to lightning weapons that we love to use so much.
The 4th King would be the leader and final encountered. It would be futile to fight if he appears and any of the other 3 have not been killed. His massive weapons would deal pure AR attacks stronger than any boss we have faced. His armor would make our weapons useless. Chip damage would be expected against him.
I took the time to make 4 sl 120 builds to mimic a small scale of what I envisioned.
Fire King http://tinyurl.com/972b9cn
Magic King http://tinyurl.com/9nw6t9t
Lightning King http://tinyurl.com/9kgcc9r
Iron King http://tinyurl.com/8lv9ej3
They all are fat roll due to the fact I feel the 4 kings are slow, besides that troll strafe where they flee a mile away lol. Also helps focus on the power aspect I am getting across here. Backstab would not work since you cant backstab a boss.
The 4 kings 2.0 behold!
What strategies would you use to defeat them, knowing that the next one is coming in a few seconds???