These would be designed for a group of 4 experienced players with good builds or 12 lesser experienced players with less good builds, would have a decent number of mechanics (NOT self healing) as well as much aoe spam to dodge, and there could be 1 or 2 per major zone. the regular world bosses would remain untouched, but these mega powerful enemies would satisfy those who want more "traditional" mmo world bosses.
They could drop a couple pieces of purple set gear from that zone per player.
Playing your character the way your character should play is all that matters. Play as well as you can but never betray the character. Doing so would make playing an mmoRPG pointless.