After playing here a while, I have thought of some ideas that would be fun to fight, instead of the 50-100 million+ hp tank and spank slugfests that are most of the bosses.
Single target Blind + Tank hate wipe
Teleport people a short distance away, into another room, like Trakanon Touch or the one used by the last dude in Txevu.
A debuff with a certain number of counters (probably needs to be 2 slots of 99 counters) that it shouldn't be instantly cured, but you can't keep proc healing and accidentally remove it. This spell should either do something bad when removed, or provide a critical buff to survive part of a fight. Yeah it might make SKs favored for one boss, but people can use single target cleric/druid/shaman heals and the paladin epic click to survive it. Example: Boss summons a bunch of adds that hit ridiculously hard, but debuff provides huge mitigation for a short duration or something so that it's survivable.
A charm that also gives a proc to the charmed player, like an AoE or a knockback or stun or something hilarious.
A debuff cast on the tank which heals the boss when the tank is struck (basically mark of emperors, numbers would need tuning). Basically the idea is to encourage a tank swap.
Adds that you DON'T want to AoE, because they explode for large (100k+) damage when they die. Ideally, they would not spawn under the boss, but instead come from a doorway of the boss's room or something, and you have a paladin or SK pick them up and offtank them.
A boss that gives a warning, then roots himself and fires off a huge aoe shortly after. Players need to run out of range of it to not get one shot.
Zombie adds that proc a debuff that aoes nearby friendly targets and reduces healing received by the affected player, the adds need to be killed by ranged damage to avoid the debuff.
Not sure this is doable, but a boss periodically buffing himself with a 90% or something buff that needs to be removed, with adds that drop an item that you can click on the boss to dispel it. The boss's buff would most likely have to be beneficial with counters, with the click being detrimental with counter removal.
This is just a start. I wouldn't mind shorter, more chaotic fights. I think they would be a lot more fun than pounding away as an earth elemental while watching Netflix, hitting dread gaze when my audio trigger for "HELP!" goes off.