When a target has a stack of status effects from conflicting elemental schools, the stacks should cancel each other out.
For example, I use my Frostbolt skill on a lion and apply two stacks of the "Chilled" status effect upon that lion. My goal is to get 10 stacks of Chilled on my target in order to apply the status effect "Frozen" on it, making it unable to move for a period of time. But then, my eager, fellow mage, raid member decides he want to cast Fireball onto that same lion. The fireball applies a stack of "Burning" on the lion. That stack of burning should cancel out at least one stack of my Chilled stacks, maybe even two.
Why? Because doing so forces your party members and raid members to actually follow an elemental ability plan, and not just throw out every AoE and skill on your hotbar without a second thought.
"But then Goalid, how can I roleplay as my Firemage igniting everyone to oblivion if I have to actually talk to and work with my fellow party members to do my rotation?! :'("
Well, there should be cooldowns on how often you can apply status effects like "Chilled", otherwise you could stack a party full of ice elemental players and keep a mob "Frozen", aka CC locked, permanently. So, when the Frozen status effect is on cooldown, that's when you start going for your "Burning stacks" in order to apply your "Melted" status effect. And you could do that by temporarily targeting other mobs or having just a hint of elemental diversity in your skills. You would work with your team, and even your raid, to weave these status effects in between their cooldowns in order to reap the benefits of each status effect.
The goal is to make players cooperate together and reap the rewards of proper teamwork and communication. Let me know what you think.
References to the Holy Wiki:
https://ashesofcreation.wiki/Status_effectshttps://ashesofcreation.wiki/Burninghttps://ashesofcreation.wiki/Chilled